Basic mode gives you one random "high" stat in addition to the one you can pick. Other classes have to be unlocked by retiring after gaining enough experience.
You use keyboard shortcuts for all exploration, but need a mouse for opening and interacting with the char sheet/inventory.
Trying to bash doors open is likely to attract monsters.
You can try to parley with intelligent monsters, distract others with food, or try to run away (if you're not wearing some heavy armor, that is).
Eventually you'll stumble upon stairs leading to a lower level of the dungeon, or fall into some trap that will take you down. If you're unlucky, it will take you multiple levels down and leave lost (meaning you will have to roll till you find a way out, hoping you won't encounter a monster that's too strong for you). Backtracking to the exit might also result in getting lost.
The town. Here you can (e)nter the dungeon again, go (h)ome and heal your wounds (each HP point for 10 GP), (b)ank your GP to get experience points (which are needed to level up and unlock new things in the town if you survive long enough to retire), visit the (m)arket and either buy supplies or sell your loot, and check dead characters in the (g)raveyard or retired heroes in the (a)dventurers' monument.
Eventually you'll find some expensive pieces of equipment, so remember to take their value into account when deciding when to retire, and to sell them before doing that.
If trying to sell some vendor trash, you also get an option to sell all of it.
The different coin types all get converted to GP once you return to town.