File, new trace.
Connect to your sql server.
Use the template -> select Tuning
select save to file -> choose a location with sufficient space
select -> enable trace stop time 10 minute of data should be sufficient move it up 30 minutes if you need. The more data you gather the more needs to be analysed.
After you have collected the trace data. Open the trace file in the database tuning advisor
on the general tab select your database and trace file. Start anaylsis.
The queries that are affecting the system will be show in the results as well as suggestions of possible index optimisation
Hope this help