After Ive cutted some "tails" off these three video clips, can I join them all in one click or keyboard combination? or i must drag them together one by one with my mouse?
Hope anyone could help because i got hundreds of these actions to do.
There may well be a way to do what you want automatically, but I'm afraid I don't know of one, sorry!
However, to avoid this situation in the future, when you highlight and cut part of a timeline object, instead of simply hitting the Delete key, hit Ctrl+Delete. This will delete the section you don't want and close the resulting gap.
Further to what Jeff said, next time, select mouse mode for a track ( shortcut 8) and when you trim with z or u or delete, the gaps will close up automatically.
If it is a case that really is more or less as simple as the one in your screenshot (i.e. just one track with clips), I think you could use batch conversion to export all the clips, and then reimport the lot into an empty project / empty track. Takes a while, but you could just let the computer work by itself.
I think i used this method in a similar case - but to be honest it was a while ago, and I am not at my video cutting comuter right now to check if that really works.
The standard advice is as given above, however, avoid creating the gaps in the first place.