I have multiple video files which were copied and pasted from other project (and they are randomly separated from each other on timeline); how can I snap all of them together in new project. thanks in advance

You can select them in Project Media and drag to desired place.

Marius,
Do you have Excalibur? If so it can be done is 1 button push. If not, then it's a much slower process. Highlight all the clips to the right of where you want them, pull to the left. Hold the CONTROL down, UN highlight the FIRST clip, pull the rest to the left, repeat. OR double click in the area of the video track BETWEEN the clips. Control F, move to the next open area repeat. It can be a lot of work.
Excalibur has a fully functional free trial. Maybe get that, try it and I'll be you'd buy the program because it's so dog gone useful. I've been using it for years and can't edit without it. Or you could do what Juris suggested. Either way.
Just a thought!

Yes, Excalibur has the Gap/Overlap feature that will certainly do what you want at the push of a button. Very easy to use.