The !give command is used to give or trade one of your items to another viewer, once given that item will be removed from your inventory and added to the viewer you gave the item.
To see the items in your inventory you need to check the available items you have in your inventory (blushyface.jppat.us:8081/Profile.aspx?viewer=Blushyface), giving an item to another viewer that you do not own will not work.
To give an item you can do this by typing !give [viewer] [item type] [item name] example !giveitem blushyface hair saiyan
The !givepet command works the same, except the items that can be given to your pet are limited to consumables to level up your pet or to boost its stats.
To give an item to your pet you can type !givepet [item type] [item name] [pet nickname] example !givepet consumables burger petname
Broadcaster and mods can give any items to viewers as well as using the !giveallitem / !addallitem command to give everyone currently in chat a specific item. example: !giveallitem other luckydrop