Cutting clips

When creating my DVD trailer I was required to cut some of the clips that I downloaded, to allow me trim and change the size, and in turn just get the sections of the clips that I wanted to use in the trailer. 
To do this I double click on the video that I want to use and this then in turn goes on the left side of the screen. I then play the video and move the play head to the part of the clip where I want to cut the video and again move it to the end to the selection where I want to end the clip. 
When at the beginning of the selection I want and use the mark in and mark out tool, shown below. The green bar that the appears in the section in the middle is the selection. 
I can then drag the clip down by dragging the picture on the screen down, I can then place this into the clips bin. The clips bin will then contain all the clips that I have cut, with the original footage still being available in the original footage bin.
The clip can then be dragged across onto the timeline and be used in the trailer.