What should I do when I have no ideas and no strategies? I'm really a beginner in chess, and I just know the rules. So many times in the game I have no idea what should I do. None of my pieces are in danger and I don't have any strategies.

What should I do at this point? Make a worthless move, like moving a pawn? Try to make some space for my knights and bishops?
This is very hard to answer since the question is very broad, but in the opening, always ask yourself "what piece haven't I moved out yet?" If you move pieces twice or three times in the opening, and I am developing each one after only one move, soon you will be fighting with only two or three pieces against me with 5 or 6. You will not win that way.

Other than that, ask yourself what pieces of yours are not defended, and make sure they are safe; and conversely, look at what your opponent has that is undefended, and see if you can take advantage of that. Not losing pieces is the biggest problem for weak players.