So, it's a rogue-like game. You wander a dungeon, beating up monsters and getting loot. If you die, you're dead. No second chances, no save games.
Use WASD keys to move, or click on the playing area for the game to move you to any square.
Right click on a monster to attack it.
Right click on doors to open them.
Hover over items to see info about them. Right click on items to pick them up. Drop them into your iventory with left click (or back on the floor with right click). Once in your inventory, right click to equip them.
When in a shop room (a room with lovely items on counters, which you can pick up if you have enough cash), hold shift and right click an item to sell it (value will come up on tooltip, but only when in a shop).
Search for stairs down to get to the next level.
Search for crafting stations to make new items.
Identify potions by using them once. Some will have ill effects. Identify items by using an identification scroll.