In Path of Exile, each item has an item level that’s hidden from the eye until you press ALT key while hovering over the item. Item level is not level requirement for using the item but rather games way to put items in tiers. Item level can be very important for several reasons:
Sockets – the number of sockets an item can have is determined by its item level – for example, item with an item level of 15 cannot have more than 3 sockets. This, however, can be overridden by crafting the item using Vorici’s crafting bench but usually is not required.
I would also like to note that not all items can have the same amount of sockets even with item level higher than 50 – only body armors and 2-handed weapons can have 6 sockets, gloves, helmets, and boots can have maximum of 4 sockets, 1-handed weapons and shields can only have maximum of 3 sockets, rings can have 1 socket.
Magic or rare items have affixes (prefixes and suffixes) that are divided into tiers – for example, to get Merciless %increased Physical Damage prefix on a weapon, it has to have at least item level of 83. All rare and magic items you can equip can have affixes, including flasks, jewelry, armour and weapons – jewels are the only exception and their affixes are not affected by item level.
The following table is the number of sockets on items with minimum item levels:
Hopefully the above guide will be helpful to you.