How do I make a Energy/Stamina bar? Dash costs 50 energy to use.

What I mean is how do I script a code where if a player uses a move they lose stamina, like if they press "q" to dash and it takes off 50 stamina points, and if they have < 50 then they can't use the move at all until their energy regens.

I've looked all over and I haven't gotten any answers to my question.