For the toilet, the top half of those flat squares should pop up and expose the screws holding the toilet seat onto the toilet. Remove the seat and scrub the toilet area with a plastic scrubbie and some type of cleaner. My choice would be Soft Scrub with Bleach.

You Tube video on removing seat

Agree with the above and would like to add that in my experience, the dust from toilet paper tearing and the skin cells that we slough off in the bathroom just build up on surfaces around the toilet and sink for those of us who do not wipe these surfaces down every week. I have some things near my toilet that just get covered with dust. Then anything on the toilet itself is sitting on colder porcelain. It is colder because of the cold water it is holding. In the humid air of the bathroom that means that water then condenses on the outer surface of the cold porcelain, mixes with the microscopic skin cells and paper fluff and powder and it just STICKS to the surface. It builds up around the tabs of the toilet seat screws because that is where the dust stops when it is blowing around the room. Any sharp angles on a toilet will do the same thing.

The solution is to wipe surfaces more frequently. I had to start buying the disinfectant wipes when I had an incontinent dog. So, now that I have them in the house, I will use them in the bathroom. I wipe the toilet flush handle, the top of the seat lid, the underside of the seat lid, the seat and the underside, then I go behind the seat and get the area you photographed. Next, I get the rim. I might use another wipe and do the door handles, the switches, the faucet and handles on the tap, then the tank lid, then the outside of the toilet bowl and use the last wipe to redo the rim if it was still not perfect. I always move from the cleanest places to the grimiest places. A third wipe would do the windowsill and the counter.

Now, I may not do all three wipes at one time, or in one day. I may see an area that is yucky and do one wipe's worth that day, then another a few days later. I also have disposable rubber gloves around and if I am in the mood to clean I will put on one or a pair and scrub the toilet and do all the wiping and vacuum and mop the floor. My goal is to not be embarrassed to let someone use my bathroom if they should drop by. I am a messy housekeeper, but I can still be a CLEAN messy housekeeper, I figure!

Oh, and I recently bought this, and it has helped and would probably help you in your shower until you can get it redone properly. It did kill mold and mildew in my old shower before we tore it out. It is the same kind of water that Toto uses to wash the sides of the toilet in the newer Washlets. Force of Nature

Do you have an exhaust fan in the bathroom? If yes, try to leave the door of the shower open and be sure to squeegee the water off the glass, off that ledge, and down the wall after every shower. You might want to use a fan to blow air around the shower after you are done, too.

Now that I am looking more closely, it does look like this might be tile in your shower. Is it? Then the top of that ledge was not made with a tilt to it to let the water run off. And the top of your bench and the ledge are too short. There is no overhang. That is why the wall underneath is all moldy, too. The water does not drip off an overhang, it runs down the wall.

You could do a couple of things. You can either order the Force of Nature kit and get the e-water that will kill the mold and mildew with less smell and a little elbow grease, or get a smellier and faster product you can pick up today at any grocery or hardware store for killing mold and mildew. Be careful, these things can hurt your lungs if you are sensitive! Clean all of the shower, get all of the mold out of the grout and everywhere. Get a squeegee and make sure everyone uses it. It would not hurt to wipe down the corners and other wettest places, too. Yes, after every shower. And then clean it regularly. Scrubbing Bubbles or any bathroom cleaner, or the Force of Nature would work.

What are the ledge and the seat made of? What is on the wall below those two? It is clearly tile above them.

I wasn't able to get back here sooner but thank you so much for all the responses!

Nancyinmich, I never realized how high-maintenance a bathroom could be. We just take showers but we don't wipe down after. I clean the bathroom once a week but it looks like keeping the bathroom dry after every use is the best thing to do to prevent these things. Our bathroom doesn't have an exhaust but it does have a window. I don't close the door once we're done because I feel like the steam gets stuck inside.

The ledges on both the divider and the floor weren't built with a tilt so water can just stand on them. Looks like I have to save up to put tile on the divider surface. I can see the cement already, too.

What is there? Is it waterproof, or is it all rotting underneath? If it gets that moldy every week, it makes me wonder if the tile itself is moldy from rot under it. Is the tile solid if you poke it?

What are the ledge and seat made of?

You say the paint and plaster is flaking off. Where is the paint and plaster? Is it on the other side of this half wall, below the glass, on the front?

If yes, the wall may be saturated and need to be demolished. Grout is not waterproof, it is porous. If the people who built this shower did not use waterproofing under the tile, then the water that sits on the tile is getting into the walls through the grout and the cement that you see. The whole shower will need to be torn out and rebuilt because it is likely that none of it has waterproofing underneath the tiles. OR, could the water be seeping under the glass and dripping down the front a bit and ruining the paint and plaster? Even a waterproofed shower would have problems with that wall if that was happening.

Does it smell moldy in there if it is closed up? You need to have someone who understands tile construction and waterproofing methods look at this. Just be prepared that you might hear that it is time to tear it out and put in a new shower. (or not!)