Welcome back^^

Item level / iLvl, aplies to some level 99 gear, but not all. The iLvl will be marked on the item, but it will also say "level 99" which means you have to be 99 to equip it. Then the iLvl reflects the power of the item, going from 99 --> 119.

ILvl weapons benefit from skill+, in the case of weapon skill +242 for example, this raises your weapon skill by that amount while the weapon is equipped. So if you base is sword skill 400, you will be sword skill 642 with a a skill+242 iLvl weapon. This doesn't show up in the skill tag in Profile, but it shows up in your attack rating and your accuracy rating.

If you are just coming back you should activate Seekers of Adoulin, and activate the Records of Eminence quest. RoE is very useful for getting stuff. People still xp in Aby Altep on sandsweepers, but also in Seekers areas. Trade your green mog pell to the Festival Moogle, mine is at wind-walls MH entrance. I picked 10 copper vouchers which you trade to the Records of eminence NPC, and convert into currencies such as sparks or delve plasm etc. I convert it to sparks usually.

Most content now is merit-points BCNM where you buy a bcnm pop using merit points, also Delve, Voidwatch, Skirmish, WoE etc. There is a lot of stuff going on. You need to get a new LS to help you re-start and do current content, because it is too vast explanations to outline in a forum box.