ok for this step to breathe in garrys mod you must first exist which to do that you must have:
2 parents
4 grandparents
8 great grandparents
16 great great grandparents
blah blah blah

ok now that you exist you must then:

grow up to an age where daddy lets you play comptuer
understand english
be able to walk and breathe
understand computer
have money
to get money you must either steal or ask mum or dad (stealing might get you in trouble!1!)

ok now that you have money and computer you also need keyboard and mouse unless if you have a laptop
now that you have money download steam off of google or microsoft edge or smth

now that you have downloaded steam open it and create an account

now you must use the money and buy gmod it cost 10 dollar

wait for it to get done

load in a map

and then breathe using the ALT+F4 key

ok thats it

ok so get in a map of gmod and press the ALT+SHIFT+CAPSLOCK+DEEZ NUTS+ key and then press W on your keyboard