Sign in Google AdWords account : Web promotion

Select your Google Account

Go to apps.admob.com and sign in with your Google Account.
We recommend using your existing Google Account connected to your existing AdSense account if you have one. If you don't have an existing Google Account, click the Create an account link to create one. Then, return to apps.admob.com and sign in.
On the Sign up for AdMob page, review the AdSense and AdWords account information associated with your Google Account and do one of the following:
If you want to use this Google Account, click the Yes, use [ your Google Account ] button to continue.
If you don't want to use this Google Account, click the Use a different or new Google Account button. Then, sign in with the Google Account that's connected to the AdSense or AdWords account you want to use.

AdMob requires you to have both a valid AdSense account and AdWords account. All future AdMob ad serving and payments will be linked to these accounts, so make sure you're using the AdSense and AdWords accounts you want linked with your AdMob account. These accounts cannot be changed after your AdMob account is created.

If you're missing one of these accounts, don't worry! We’ll help you create them during this sign-up process.

Review or complete your AdSense information

Existing AdSense account

If you want to use this AdSense account, click the Yes, use this AdSense account button.

If you don't want to use this AdSense account, click the Cancel button and do one of the following:

Cancel and close the AdSense account. Canceling your account should be a last resort reserved for inactive accounts that aren't currently receiving ad requests or generating revenue. Please note that if you cancel the account you will lose access to the account data. If you don't see the option to cancel your account when you sign in to AdSense, please contact AdSense support.

New AdSense account

If you don't already have an AdSense account associated with your Google Account, you'll need to provide some information for AdMob to create one for you. Please note that your new AdSense account will have limited functionality.

Source: support.google.com