Help with jumping

Questions
1

I am currently making a sidescroller game where my person needs to be able to jump once every time I tap the screen. I have been thinking and thinking about this but nothing I try works. Could anybody please help me.

2

If your person is a physics body then just give it a velocity upwards when the screen is touched. else if the sprites position is defined by something like SpriteX and SpriteY then maybe you could increase the SpriteY when the screen is touched.
Something like this:

function setup()
    b=physics.body(CIRCLE,20)
    b.gravityScale=1
    b.x=WIDTH/2
    b.y=HEIGHT/2
end

function draw()
    background(0, 0, 0, 255)
    if b.y<20 then
        b.gravityScale=0
        b.linearVelocity=vec2(0,0)
    else
        b.gravityScale=1
    end
    if touches then
        b.linearVelocity=vec2(0,200)
        touches=false
    end
    fill(255, 255, 255, 255)
    ellipse(b.x,b.y,40)
end

function touched(touch)
    if touch.state==ENDED then
        touches=true
    end
end
3

Don’t set the linear velocity, then if the player was moving it would stop. Use body:applyForce(vec2)