how do i fix my macintosh computer

That is seriously unclear. Try to explain a bit better, kthx.

 

Have to agree with Verix, but I think what the problem you have is.

Your losing space on the Hard disk/ssd without using the computer, computer is on.
Are you using TimeMachine, if both are true it is TimeMachines local backup using the space on your disk.
When was the last time you backed up your machine?
Now, I do not use TimeMachine but I think it will get better after using TM again.

 

Can you be more precise? We actually do not understand what your problem is, and that English is probably not your first language, which probably makes it harder for you to describe the problem of yours.
Maybe try it once in English and then again in your mother's tongue, maybe someone can chime in.

"How to maximise your MacRumors troubleshooting experience" created by mad jew in 2006​

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This one here makes me think, that you speak about an internet connection and data usage (uploaded and downloaded data):

And modifying your signature now may not really accelerate the solution of your problem