Fields: Fields are nothing but the columns in the regular database. There are two types of fields: Standard Fields and Custom Fields

Standard Fields:  There are the fields which are created by salesforce or the default fields which are given by salesforce. These fields cannot be deleted. We can customize the fields. Some of the standard fields are called System fields.

System Fields : There are the fields which are created by salesforce and updated by salesforce. There are seven types of System Fields 

ID:  Salesforce by default creates 15 Character unique Id for every record. Salesforce will recognize the record by using this Id. First Three characters of Id will represent objects. The Last Four characters of Id will represent records.

15 Character Id is case-sensitive. By Adding three more characters it will be case-insensitive(18 Character Id).

isDeleted: Whenever we delete any record, the value of isDeleted field is set as True.When we delete any record it will still be in the object for 15 days.

After 15 days records are permanently deleted.

CreatedById: This field will store the 18 character Id of the user who created this record. 

LastModifiedById: This field will store the 18 character Id of the user who last modified this record. 

CreatedDate: This field will store the date and time when the record was created.

LastModifiedDate: This field will store the date and time when the record was lastly modified manually.

SystemModStamp: This field will store the date and time when the record was last modified manually or programmatically. CreatedById, LastModifiedById, CreatedDate, LastModifiedDate, SystemModStamp are called as  System Audit Fields

Custom Fields:

These are the fields which are created by the user to meet his organizational business requirement. Salesforce has defined predefined data types to create the custom fields which are mentioned in the below

Text:

Format: Alphanumeric

Maximum Length: 255 Characters

Single|Multiple: Single Line

TextArea:

Format: AlphaNumeric

Maximum Length: 255 Characters

Single|Multiple: Multiple Line

TextArea(Long):

Format: AlphaNumeric

Maximum Length: 1,31,072 Characters

Default: 32,768 characters

Minimum Length: 256 Characters

Single|Multiple: Multiple

TextArea(Rich):

Format: Formatted Data

Maximum Length: 1,31,072 characters

Default Length: 32,768 Characters

Minimum Lines: 10 Lines

Phone:

This data type is used to store the phone numbers.

CheckBox:

These data types will store the value of true or false.

Currency:

Currency values are  stored in these fields.

Max Length: (Length of Integer + Length of Decimal) should be at max 18 characters.

Ex: 32000.20 ( 5+2= 7)

Date:

This field will  store a particular in the calendar.

DateTime:

This field will store the particular day and time from the calendar.

Number:

These fields are used to store numeric values 

Maximum Length: 18 characters( Length of Integer + length of Decimal)

Percent: 

These fields are used to store the percentage value ,by default ‘%’ symbol is appended to the data.

Maximum Length: 18 characters( Length of Integer + length of Decimal)

Email:

These fields will store the email id’s. Salesforce has defined validation rules to check the format of the email address.

PickList:

It is a dropdown list from which  we can select one option at a time. Maximum we can  provide 1000 options. Length of each option can be 255 characters. 

All the options together can be 15000 characters. We can sort options in the ascending order. We can make the first option as default option by enabling the checkbox. We can add /remove/edit /reorder the options  based on business requirement.

PickList( Multi-Select):

It is also a picklist field but we can select more than one option at a time.

We can provide a maximum of 150 options. Maximum we select 100 options from 150 options . Lengths of every option are often at max 40 characters. All the options together can be 1500 characters.

Text Encrypted:

When we want to save sensitive data then we define it as text Encrypted. Maximum length of the field is 175 characters.

By default nobody can access the info within the original format. If you would like to ascertain the info within the original format, users profile should have 

view encrypted data permission enabled. Text encrypted fields can not be used in formulas. Encrypted fields can not be used in search Criteria or filter Conditions. Encrypted fields can be used in validations, search results, report results.

Custom Fields Creation:

Custom Fields can be created in four ways 

1.Standard Navigation 

2.Schema Builder

3.Force.com Quick Menu 

4.Metadata SOAP API web service

Standard Navigation:

Classic:

1.Click on Setup

2.Click on Build

3.Click on Create

4.Click on Object

5.Click on Object Name

6.Click on Custom Fields and Relations

7.Click on new

Lightning:

1.Click on Setup

2.Click on Platform Tools

3.Click on Objects and Fields

4.Click on Object Manager

5.Click on Object Name

6.Click on Fields and Relation

Creating custom fields:

1.Choose the dataType 

2.Enter field Details Like (Label,Name,Required, Unique)

3.Next

4.Next

5.Save

Schema Builder Navigation: 

Classic:

1.Click on Setup

2.Click on Build

3.Click on Lightning Bolt

4.Click on Schema Builder

Lightning:

1.Click on Setup

2.Click on Platform Tools

3.Click on Objects and Fields

4.Click on Schema Builder 

Creating custom fields using Schema Builder: 

1.Choose the Object 

2.Choose elements

3.Choose the dataType

4.Enter the details 

5.Save

If we create the fields using Schema builder fields are not added to page layout. We need to manually add the fields to the page layout.

1.Click on Setup

2.Click on Build

3.Click on create

4.Click on Objects

5.Click on Object Name

6.Click on PageLayouts

7.Click on Edit

8.Click on add the fields

Force.com Quick Access Menu:

1.Click on the Tab of the object

2.Select Force.com Menu

3.Choose view fields

4.Select Custom Fields and Relations 

5.Select new and create the fields.

Field Dependency: If the value of one field is controlled by another field then we call it ashfield dependency.

Controlling Field: We can choose any of the PickList Field or Checkbox fields as the controlling field. If we choose any picklist field as the controlling field ,then picklist field can have a maximum of 300 options in it .

Dependent Field: We can choose PicklIst /MultiSelect PicKList field as Dependent field. We can create multi level dependency.

Steps to create field dependency:

1.Click on Setup

2.Click on Build

3.Click on Object Name

4.Click on Custom Fields and Relations

5.Click on Field Dependency

6.Click on new

7.Select the Controlling Field

8.Choose the Dependent field 

9.Include and Exclude the dependent options for the Controlling Field.

10.Save.