Every magic item has a rarity that signals how powerful it is and roughly what level it suits: common and uncommon for low levels, rare for mid, very rare for high, and legendary for the most powerful gear. Artifacts are unique, story-defining items outside the normal scale.
Rarity also guides price. The Dungeon Master’s Guide gives rough value bands — common items are worth tens of gold, while legendary items run into the tens of thousands. These are guidelines for buying and selling, not fixed prices; your DM sets the final number.
Rarity is separate from attunement. Some items require you to attune during a short rest before their magic works, and you can be attuned to at most three items at once. More powerful items are likelier to need attunement, which stops a character from stacking too many bonuses.
To compare your item with official ones, browse the full list of SRD magic items or the lists of uncommon, rare, very rare and legendary items.