Types of Objects
Standard Objects :
These objects are present by default in salesforce.
For Ex: Account, Contact, Leads etc •Salesforce provided these standard objects as they are used by most of the businesses.
These are the objects we create based on our requirements.
Types of Fields
These fields are present by default in salesforce when you create a custom object or also there in standard objects.
These fields cannot be deleted.
For Ex: Name, Owner, Created By, Last Modified By
These are the fields which we create to meet our specific requirement.(in case of custom objects).
These fields can be deleted