General:

!help - Gives a list of commands like this.
!how2trade - Guide on how to use and trade with the bot.
!price [amount] <name> - Get the price and stock of an item.
!rate - Shows what the bot values keys at currently.
!buy [amount] <name> - Instantly buy an item.
!sell [amount] <name> - Instantly sell an item.
!stock - Get a list of items that the bot has.
!queue - See your position in the queue.
!cancel - Cancel an already made offer, or cancel offer being made.

Buying or selling multiple items:

!cart - See current cart.
!buycart [amount] <name> - Adds an item you want to buy to the cart.
!sellcart [amount] <name> - Adds an item you want to sell to the cart.
!clearcart - Clears the current cart.
!checkout - Make the bot send an offer the items in the cart.

Instant accept if the offer is correct.

If you want to donate, add "gift" or "donate" in trade description, otherwise trade will be declined.

In case there's problems you can't solve by yourself, try to contact bot's owner.