Ramuh Summon Location and Guide
The Ramuh summon becomes available after you acquire the Purple Chocobo or the Airship on World 1. Once you make it to World 2, this Summon is missed forever and you'll never be able to get it on this game file. You'll find Ramuh by roaming around in the forests next to the town of Istory (Ps1 Translation calls it Easterly) as a random encounter.
He's usually the first thing that will attack you when you're in this area so you won't have to search long to find him. Don't use Lightning attacks against Ramuh since that's the same element as him. I'd recommend you don't use magic at all since he has pretty high resists but if you have to, use anything but Bolt.
After defeating Ramuh go into your inventory and find the item named Ramuh and use it; get used to doing this when you fight a Summon, there's more than 1 that will appear as an item in your inventory. You'll have the summon after use the item in your inventory - congratulations!