remove parts of the song , see the description above to select a part of the track, and choose Delete in the right click menu
change the mix in/out point by moving the transition window. Drag the olive colored bars in the transition window or the blue colored transition window to the left or the right
You can speed up your mixing process by using keyboard shortcuts. You can find the explanation of all of the shortcuts in the middle bar at the right side of your Studio.
For even more Advanced editing options, you can also use the Sample lane.