list of queries fired on database in a given timeframe

Hi,

I am new to SQL server. I want to get a list of queries fired on a database in a give timeframe. Basically, I have been assigned to a project which uses SQL server and they are facing some performance issues.

So I would like to find what are the top 5 or top 10 queries that are being fired on database, so I can mainly focus on optimizing those queries etc. For this reason I need a list of queries fired on the database. 

Is there any log where SQL server keeps this information so I can readily fetch it?

Looking forward to your response. Thanks a lot!