For build path in the android studio look like different in eclipse user.
For adding others SDK ( like Google admob sdk ) in an android studio on your application Project. simple doing flowing this steep.
File -> Project structure -> Modules -> Sources -> Add content root
First, select your project Go to File and Select Project structure option
On Project structure Windows See [Project Settings] you can select [module] on module section you can see [ + add Content Root ] by clicking opening a new window [select content root directory].
Here you can select your sdk location (.jar) file .
Select file and click OK .
Finally Adding your sdk location click Apply.
Done you can successfully add sdk on you project 
