Magic Lamp Location and Guide
The Magic Lamp is a powerful item which allows you to use every Summon in the game (at least once) even when your character isn't a Summoner. Once you make it to World 3 and reconnect with Boko, your Chocobo companion who you abandoned earlier in the game, you'll be able to collect this item whenever you please.
To get to this location you'll want to hop on Boko and travel to the northern-central portion of the world map. Even though you see the Magic Lamp to the northwest, you won't be able to reach it that way due to mountains almost entirely blocking it off. Instead what you need to do is run across the rivers which connect the waterfall that you find the Magic Lamp at to the north-central portion of the world.
If it sounds like finding the Magic Lamp will be complicated, I assure you - it's not. You won't have any battles while on Boko so all you need to worry about doing is finding the river's mouth and following it. Best of all, they designed the Final Fantasy V world map in a way which you can't get stuck anywhere with Boko. There's pathways which will let you run him around almost the entire map in a large oval.
The Magic Lamp is fairly straight forward with how it works. Each time you use it, it'll summon a different summon starting with the most powerful summon in the game (Bahamut) and ending with the least powerful, Chocobo. To make things easier for you, here's the order of summons you'll see come out of the Magic Lamp...
Once you consume some charges on the Magic Lamp, you'll be able to recharge it one of two ways. You can return to Istory Falls where you originally found it or go to the Great Sea Trench in the submarine and recharge it there. In addition to this, there's two more things you should know about the Magic Lamp. First, it doesn't use the Phoenix Summon. Second, when using the Odin summon, he won't use Gungnir instead he will use Zantetsuken. Also, in the PS1/English versions I don't think the Eggman Summon works/has a sprite.