You can't, you must evolve a Larvitar.
In Pokémon LeafGreen, you can find Pupitar by evolving a Larvitar, which is located in the Safari Zone. Larvitar evolves into Pupitar at level 30. Note that Larvitar is relatively rare, so it may take some time to encounter one in the Safari Zone.
You have to trade from LeafGreen/FireRed.
You find larvitar in seavault cannyon. and then you evolve him into pupitar and tyranitar :) check serebii.net if you're wondering.
Catch a lavitar at island 5 and train it into a pupitar and eventually in the Pokemon league it should evolve into a tyranitar.
It's actually impossible to catch Pupitar in Pokemon Emerald. The only way to get it is to trade it from LeafGreen and FireRed. Hope I helped :)
no no no might be
Pupitar is a Rock and Ground type pokemon.
Trade it from firered and leafgreen to emerald.
You don't find it. You find larvitar, which is located at Mt. Silver.
You get pupitar by evolving larvitar.
Piplup does not exist in Pokemon LeafGreen or FireRed.
No, you cannot find cyndaquil in LeafGreen.