There is a paragraph about Trim in the wiki:
Using_TrimThis command uses an entity for reference, where the modified entity is shortened/lengthened to. The reference entity is not modified with Trim command.
The Trim Two command modify both, the reference and the second entity. Use Trim Two on two crossing lines and both lines will be shortened to the intersection point. Depending on the position where you click the lines the result may be different. The part of the line where you click is kept, the part behind the intersection point is removed.
Armin
investing less than half an hour into Search function can save hours or days of waiting for a solution