I had a kitty, and then it disappeared,
While your starting pet is quite often more combat-capable than you, it can be killed easily by a stone fall trap. You'd see a stone lying on the ground it that's the case. You will get messages like "you have a sad feeling for a moment, then it passes" - which means your pet died outside your view. Or variants for other cases.
Or your pet can be lost through a trap hole on the ground... it will be sent down a few levels (randomly chosen), and you might find it again later when you visit those levels. You can tell by the message of "noise in the distance", meaning your pet is fighting monsters on the same level.
and I have an inventory, but I don't know how to use anything. I pick up everything automatically, even if I have no concievable use for it. And there are a bajillion commands.
For inventory commands, you will use these most often:
A - Remove a bunch of equipped items. You will get another menu to choose from.
a - Apply. Used to activate items like lockpick, unicorn horn, bags, etc.
d - Drop a single item.
D - Drop a bunch of items. You will get another menu to choose from.
w - Wield. For equipping weapons.
W - Wear. For putting on shirt, armor, helmet, boots, gloves and shield.
P - Put on. Used for equipping blindfold, towel, rings and amulets.
R - Remove. Opposite of P.
Q - Quiver. Assign a stack of items to be used when you use the f (Fire) command.
x - Switch primary and secondary weapons.
Oh and you don't want to pickup everything. Encumbered you will act slowly (monsters will get to move more frequently than you do) and you will fall down stairs (which is a lot more dangerous than it sounds for some situations). Edit defaults.nh to pickup light items only (read Guidebook.html to learn how to edit it).
I have this:
OPTIONS=autopickup,pickup_types:$
To pickup gold automatically. You might want ! for potions, = for rings, " for amulets too. # for spell books, but they are heavy.