Touch can be detected by Touched event, might need to look into some examples to see how it actually works on players, since characters are models that consist of multiple parts, touched trigger multiple times.
Bringing a character to a separate field isn’t necessarily teleporting them there. In most pokemon games, when an encounter is triggered, the character remains in the original position to avoid further teleporting back and forth, and instead creates a duplicate, uncontrollable character in the new field where the player press buttons to command the character/pokemon to perform actions.
If you are really a beginner, turn-based combat systems might be too much but if you really want to make one, learning is the only way. Good luck!