How do you make projectiles?

I was going to try and make a diep.io clone to learn how to code since im super new but I ( and apparently chatgpt) have 0 clue how to make a projectile that doesnt fly toward the floor. Any method works, i just wanna learn the skill irrespective of how to get there. Ive all but given up on the original code im having issues with, ill just re write it from scratch. I just wanna know how