My shower is draining VERY slow
Have you cleaned the hair out of the drain? If not do it with a pair of tweezers. Then flush with very hot water.
Have you used one of those hair grabbing sticks like the Zip it?
Lowe's sells a skinny little gadget for this purpose for about $3.00- $4.00 . Mine is yellow, about 18 inches long with little barbs on the side. You wiggle it down the drain, then pull up; the hair catches on the barbs. Might take 2 or 3 tries to clear it all, but this is a quick, easy, and cheap solution. :)
The gadget they are talking about above works but I have just been using my toilet plunger periodically and it has worked fine. Of course you should clean your shower afterwards.
Try to lift or unscrew the cap. Inside should be a basket with all the gunk in. Dispose of gunk and clean and reset the basket and cover. If you don't have a drain with a cap, use something like Vinegar or bleach to dissolve the obstruction or make a hook in a piece of strong wire and push that into the holes to try to hook the stuff out. Best wishes.
Get one of those plastic drain cleaners with the pointy parts and yank out the hair. After that dump in baking soda and vinegar. You may have to repeat the latter a couple times.