If the clip is in the bin (at the top-left), move the red cursor in the preview window to the desired start point. Click the Set Start button.
Move the cursor to the desired end and click the Set End button.
Then click the caret to the right of the ADD button (under the PV window) and choose where the trimmed clip will be added to the timeline...
It can be further positioned by dragging it on the timeline.
If the clip is already on the timeline, position the cursor at the desired start point and click the scissors or click Split button...

Do the same for the desired end point. Now a new clip has been created between those two splits. It can be deleted if desired.
If you make a mistake, click <ctrl-Z> (same as Edit menu | UNDO) to go back, step-by-step.