A slow shower drain can be really irritating. Especially once it gets to the point where you will be standing in dirty water while taking your shower. The reason for this problem is usually a clog consisting of soap and hair, unless you for some reason washed something else down your shower drain that you shouldn’t have.
Sometimes, it could be enough to run very hot water down the drain for the plug to dissolve, and since that is the least invasive solution, that should be the first thing you try.
If that doesn’t work, you should try to dislodge the clog using a drain snake. If you don’t have one, you could create a makeshift snake using a metal hanger. You should be careful not to damage the plumbing. If that doesn’t work either, you might be more successful using a plunger, but you shouldn’t apply too much pressure to avoid damaging the pipes.