In Pokemon Red Version, you are allowed to choose one out of the 3 starter Pokemon. Well, I chose Charmander but now I am confused as to how I can catch the other 2 starter Pokemon. Does anyone know how?
if you want everything legitimately, you'll need to trade with someone else, it's plain and simple.
It's the same for several other pokemon, which aren't available in Red but are in Blue (or yellow).
Some pokemon also evolve only during trading.
This is to encourage people buying the other game as well (and another gameboy) this is called 1 game for the price of 2.
I believe the yellow version, you can get them all. You start with a Pikachu, then through the game get given, win or find the other primary Pokemon: Charmander, Squirtle and Bulbasaur. Like others have said if you didn't want to buy a new game, you'll have to trade with other people, or between your devices with your other games.
Unfortunately in red and blue you only get that one you choose.
This only works in Pocket Monsters Red/Blue.
Actually, in Pokemon red/blue, you can legitimately catch all 3 starters. Just look in ur pokedex. Charmander/Charmeleon/Charizard u can catch in Cinnabar Island Pokemon Mansion (Charmander/Charmeleon fairly common and Charizard is very rare), the Squirtle family you can catch in Seafoam Islands (you have to walk in the cave not surf) and the Bulbasaur family you can catch at the Victory Road entrance area (probably in the grass, but idk for sure yet cuz I haven't gotten there yet, I've only caught Squirtle, charmeleon, and I have the Charizard I received from Prof. Oak as a Charmander. I will post an update on any information on where to catch the Bulbasaur family in the comments section of my answer. Red/blue/yellow are the only 3 Pokemon games where u can get all 3 starters without cheating.
Source: based on experience as I am doing a play through on my Pokemon red on my game boy color atm