Leveling is probably the most important thing you need to learn about
right now.  Since you took the old style way, you need to know what does
what and why.  When you level, your intelligence, wisdom, and constitution
(int, wis, and con on score) determine how many hp and mana you get.  If
you have a low con, you won't get very many hitpoints.  If you have a low
intelligence, you won't get very much mana.

The problem is that you need to have a high wisdom so that you can get a
lot of practices, because you use practices to train int and con at the
trainer.  You'll want to get your wisdom up to 20 as quick as you can,
then up to 22 soon afterward.  At 20, you will get four practices per
level, while at 22 you can use equipment to boost your wisdom to 27.  At
27 wisdom, you will get five practices per level, which is very important.

One cool thing is that if you are wearing equipment that raises your
stats when you level, you get that bonus afterward even if you dont keep
the equipment on.  This is what people mean when they say you should have
a set of 'leveling' equipment, which is only used when you intend to gain
levels.  The most powerful characters on the game usually have the best
sets of leveling equipment.

For starters, you should get two mud school diplomas, which are +1 wis
and +1 con each.  You can hold one, and wield the other one while leveling.
I've also given you that dragonlance book (which you can wear on your
hands), and two lockets (which you wear on your neck).  Those items will
help boost your stats when you level, and will be the start of your
leveling equipment.

For more help on leveling, you should take a look at the help pages for
intelligence, wisdom, constitution, and other words like train, practice,
etc.  Knowing whats on those pages can really help you make a strong
character.  (If you had chosen the other leveling option, things would
have been simpler, but this will provide a stronger character if you
can stick to it.)

Oh, before I forget:  after you level, its usually a good idea to take
off your leveling equipment and put your regular stuff back on.  Leveling
equipment usually sucks to fight in, and you can get killed that way.