If you just want to trim a clip, then you go to the Timeline, place the select clip in, which you can do by selecting the clip, going up to the Clip menu in the task bar, and selecting Add to Timeline. Select the clip in the Timeline and then use the playback indicator to go right to the spot in the clip where you would like to trim it. Place the playback indicator at the beginning of the part where you would like to trim the clip, then go to the Clip menu in the task bar and select Set Start Trim Point. Likewise, at the end of the clip trim set the playback indicator, go to the Clip menu and select Set End Trim Point. If you want to clear out the trim points that you set, go back to the Clip menu and select Clear Trim Points.