I just bought a lvl 5 magikarp from the sales man and I can't even battle with it. Any ideas on how to evolve it?

Hello @Strykermaximus.

 

If you speak with the NPC that sold you the Magikarp and show him a Magikarp, he will teach it one of the following moves: Bounce, Dragon Rage, Hydro Pump, or Reversal. This can help you train your Magikarp.

Furthermore, you can train it by switch-training. Though this method is not very efficient, it can help. Switch-training is when you start off a battle with a low-level Pokémon, then switch over to another Pokémon that can win the battle. Thereby, allowing both Pokémon to receive EXP.

Magikarp will evolve into Gyarados when it reaches level 20. Though, most players would suggest you not to evolve your Pokémon too early. This is because evolved forms take more EXP per level compared to their unevolved forms, thus making them harder to train. But this is only a suggestion, not a rule. Play the game however you see fit.

 

If you have further questions or require further clarification, please let me know.