You need to select using your control/cmd key.

p_rvictor wrote: Thank you nant!

Would you show me please where exactly to find control/cmd key?

Google is your friend.

p_rvictor wrote: I remembered what is the cmd key without Google. Google is very usfull thing, but I think it's much easier if you tell me of which folder or file exactly, what cmd key to put, if you know of course. Thank you!

Well than I have no idea what your issue is.

You started this thread stating:

I can not select more than one option in my "Community Builder: Edit User [dani],
Group -":

And now you are asking for folders and files exactly????

Sorry, I have no idea what your issue is anymore.

If, as in your screenshot, you are trying editing a user in CB User Manager and want to assign the user to multiple Joomla groups, you need to hold the control/command (control if you are on windows, command if you are on mac) and click the mouse one each group you want.

If the key is pressed the groups you click on will be highlighted.

If this does not help, then I can only suggest to find someone speaking your language that can understand English and help you.