Does Anyone know how to make a sprite jump on the press of a button?

I want to make my sprite jump with a position_y variable but I am having some trouble doing so. I can make it jump but it will stop in midair if the button is let go. How do I fix this. P.S. I am using micro script.

to my knowledge, you need another variable for gravity that when you click jump it will increase sharply and when jump isn't pressed, gravity is constantly decreased. you'd have to be constantly adding gravity to position_y