Hi Nasreen,
To be able to access the API, you need an AdWords manager account. Please refer to
this guide to create one.
Once the manager account is created, please follow
these steps to create a developer token. Developer token is associated with a manager account (MCC) and could be used to access AdWords accounts under manager account. While your developer token is in the approval process, you can still use the token to make calls against
test accounts (you will also need an OAuth token too, the process for which is outlined in the same link).
Once your developer token is approved, you can either create a new AdWords client account or link an existing client account to the manager account.
This guide has the steps that you need to follow to achieve the same.
Please let me know if I can be of any further help!
Regards,
Vishal, AdWords API Team