The red and blue SET brackets appear only in Clip preview mode, not Sequence mode... 
To edit clips on the timeline (Sequence mode), use the split scissors on the cursor
or the split button... 
Create a split at the head and end of the desired material, then delete the unwanted clip fragments.
Or place the mouse pointer on the red cursor and drag, to create a blue selection. Right-click in that area and Delete Selected Region. This isn't always precise.
If you make a mistake, immediately press <ctrl-Z> to go back, step-by-step.
Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. From the HOME tab, the AS choice is available by clicking the caret to the right of the Save Project button on the toolbar. That way you're protected, and shouldn't lose anything.