Thanks for playing!
At the top left of the screen is some statistics about your framerate and how many robots exist at that moment, these are mostly debug things.
At the top right of the screen, is the ammo and health bars. These show how much ammo / health you have left and the ammo bar shows your current ammo for that clip.
The box next to the cursor when reloading shows how long you have left until you have finished reloading.
The bottom left shows the timer, so how long you have played for, and if you have bought any perks, which ones you have bought.
The bottom centre shows what gun you have equipped and how much ammo you have. Additionally it also shows you what you can buy if your close enough to something that can be bought.
The right of the screen shows your score. This value allows you to buy stuff such as perks, guns, ammo and doors.
Hope this clears things up a bit for you!