How to map lead fields to Account, Contact and Opportunity while converting leads in Salesforce?

Salesforce Lightning Experience:

1. Go to Setup.

2. Select Object Manager.

3. Select Lead object.

4. Select Fields & Relationships.

5. Click "Map Lead Fields".

6. Select the fields to Map.

Salesforce Classic:

1. Go to Setup --> Customize --> Leads --> Fields.

2. Click "Map Lead Fields" button.

3. After mapping, click "Save" button.