[k-krack]

just count how many beats are in one bar like...ill do an example of a couple of times.
3/4- boom bah bah boom bah bah boom bah bah
1 2 3 1 2 3 1 2 3 1 2 3

4/4- doot deee bah boo doot deee bah boo
1 2 3 4 1 2 3 4

5/4- yip yip yeah yeah yay yip yip yeah yeah yay
1 2 3 4 5 1 2 3 4 5

It can be really tricky awhen yr just starting to... (as if it is a profession or something....haha) ...do it, but it gets easier if you listen to alot of 'math rock' (haha..)
It's super hard (for me) to actually be trying to play music in different time signatures without someone else to count it.

*Edit.. i just realised that the spacing i did did not show up... well, i hope you can rfigure it out from there...