Glad to see a new mapper in the community :)
It's a good start.
Here's a few tips:
When making walls it's recommended to make them 128 units high. Some textures will repeat them selfs if any higher. (mainly wall textures)
For example: In your 3rd screen, your wall in the middle, the brown stuff is the top of the brush you chose and since your wall is higher, it starts again.)
If your wall is 128 units high and the texture is still unaligned do as TheBucket said with aligning.
Note: You may find selecting your wall and hitting "Shift A" to be much easier. then hitting the "texture tool" icon.
If you want to make a wall that bullets can't shoot through, a wall 16 units thick or higher will stop any bullet.
I look forward to seeing your work!
Pros: This is actually a pretty good start for your first map. I like the 2 levels and the glass. The steps are not to bad either.
Cons: The map is a bit bare but you already know that. You need to add some props and safe spawn points.
Improvements: First improvement would be to add some props and maybe some inner walls to protect players from the enemies. If you don't know how to add props just send me a message and I will walk you through it. Example, Screenshot 2. See how the lights just appear on the wall. If you add some props as light fixtures it would give it a more realistic look. As for the steps, the best size for steps is between 8 & 16 units tall. I like to make sure the steps are wide enough for players to pass each other because it really sucks to get stuck behind another player that blocks the stairs. One last tip if I may. Screenshot 1, the texture on the inner walls need to be lined up. Try this, click on one of the inner walls to highlight it, then click on your texture tool. Some tabs with the letters L T R B C and fit will be on the right side. click the T tab and it will align the texture at the top. B for bottom and so on. Experiment with it.
Notes: The anonymous person that left you feedback was a very poor example of what feedback is for so just blow those kind of comments off and don't let it keep you from building your map. It takes time and patience to perfect a map. This good map will become a great map. I can feel it, lol. Keep up the good work mate.