Mac - don't go to sleep

My mac goes to sleep (goes black) and then my other pc's/laptops can't see it etc.

Is there a way to not turn it off.

I want specifically to keep it on so my LIve book duo can be accessed to be able to copy files to it.

it seems like once it goes dark I can't get to it (this also occurs when my mac air goes to sleep, my mack can't get to it).

There must be a setting somewhere.

Thanks.

 

perfect

THANK you soo much.

I was searching...but not with the right word!