Create / Delete A Field

Standard Object :- Which is already provided by salesforce. Which is predefined in any Sandbox.

Accounts, Contact, Lead, Opportunity, Quotes. These are standard object which is provided by salesforce.
Firstly Login with any sandbox then click on the All Tabs
Or
Go to setup ----> App setup ---> customize ----> Accounts, Quotes ----> fields

Then Click on the Account Standard Object.

Then click on the arrow on the top right side

Then click on the view fields

Its display the account field details. These are standard salesforce Account Object fields.

These are the custom fields. Then click on the new button for creating the new fields in salesforce.

These are the data type user can create the field According to our requirement.

Suppose we choose the datatype as checkbox then click on the next button

Then click on the visible checkbox (we have provided the Permission to this field for all given profile)

Whenever we click on the visible checkbox then all Profie are checked then click on the next button.

Then click on the save button, field is created.

Custom object::- user can create this object according to our requirement.
In custom object always use prefix __c with object name.

How to add field in the custom Object in salesforce.

Click on the All Tabs:
Or
Go to setup ----> App Setup ----> Create ----> Objects

Then click on Background Check Order Object.

Its display the recent created orders. Then click on the any order number.

Then click on the view fields for creating the new Fields for Order Object:

Then click on the new button for creating the new field on Background Check order Object.
Its same as I already explain for Standard Object.

How to delete the fields from Custom Objects.

Go to All Tabs ----> Click on Any Custom Object
Or
Go to Setup ----> Create ----> Objects ----> Click on Any Object

Before deleting the field from the object we should aware this field is not using anywhere in Apex class or VF page.
If field is using anywhere then we can't delete the field.

Then click on the del button for delete the field from Account Object