FFX2

I realy need some help. Im on ch.5 in the beginning, when i first jump into the hole that will take me to the fare plain, and i dont know what to do. When i get into a fight with the monsters in the far plain it always sais that they are emuned to my attacks. Yuna is on lvl.40 ,and Pain and Rikku are on lvl.41. I dont know what dress spheres i need to use and im at a compleat loss when it comes to hurting them in battle and can someone please tell me what in the worled is a Nule? ( And yes this is my first time playing a ps2 letalone Final Fantasy X-2, so ya im a noob, lol im sutch an ideot i didnt even get the Final Fantasy X, befor this one so i REALY need help with this. lol please anybody!?