2.) Click on [Create an Account]
3.) Signup with your username and e-mail address.
4.) Set a really strong password (always)
5.) Verify your e-mail address and thus account.
6.) All of those sites have multiple wallet addresses that are automatically created for you when you verify your account. Find your BTC address.
7.) Shoot whatever BTC you want to purchase DOGE with to address from step 6
8.) Wait for confirmations.
9.) Purchase your DOGE's.
Easy peasy!
BTW, recommend also enabling 2-factor authentication as well for security reasons. Especially if working with a large number of coins.
Hope this helps.