Welcome to the forums @"Taiyo Pixels"!
That is a big question, and one that is likely too large for anyone to answer in one go. I would suggest looking for tutorials for Godot Mega-Man-like projects using search terms like "Godot Mega Man tutorial". If there are no tutorials or you do not find tutorials you think would be helpful, then I would suggest taking the design of Mega Man, break it down. You can break it down into smaller, more achievable steps, like making the player move or adding projectiles, and then slowly put these pieces together over time until you have all of the main mechanics of Mega Man.
