How do I make a spell that puts a player on flames when you chat a spell then click a person?

I want to make a game based on witches, vampires and werewolves and I want to make a spell that ignites a player on fire when u type a word then you click someone and you have a magic GUI that when you use the spell it takes 15 magic away from you. I also need to make a magic bar that consists of like idk 300 magic or whatever but i don't know how to make that either but yeah and the spell damages the player by 20 and has a cooldown of 10 seconds and when you try use the spell while on cooldown then it gives you a message on the bottom right of your screen saying the spell is on cooldown and says the amount of time left then when you can use it again it gives u a message telling you that you can use it again. I know its a lot but I really need the help?