First off,try reading through those tutorials again.Seems like you skipped them.
Second,when you learn from the tutorials,if you are in the beginning of the game,draw magic from enemies and juction the magic spells you have to your stats to increase them.That makes your physical attacks,HP,magic power and immunity increase,so you don't have to rely on GF's so much.

Personally,my first playthrough was a mess,I only relied on GFs,I didn't get the junction system and my game was pretty much stuck in some parts and kinda boring just using GFs all the time.On disk 4,when time started compressing I pretty much quit because I knew I was weak and I couldn't defeat Ultimecia.I started all over again.

My second playthrough,when I figured it out the junction system,went smoothly.It's pretty easy,really.Just know how to junction,level up so your GFs can learn abillities and that's it.The thing is,in this game you don't have to level up to increase your stats,just junction.
So you can be level 15 and make 5000 of physical damage.

There are abillities that your GFs can learn so you can refine useless itens you win in battle,to magic spells.So you don't have to draw constantly from enemies.