Hi @CreativeCoder good question! I've wondered how to make bounce too. I learnt from a great tutorial by @Funky_63_Greenland and here it is:
So like @Phase_Studios said, you can call the value "Gravity".
At the start, set Gravity to 0.
Increase "Gravity" by -1
Change Y by "Gravity"
(in the picture it says repeat 99999 because there weren't any repeat forever blocks at the time, and the Increase Value block used to be called Change Value).
And when you want your object to bounce, add the code:
Set value "Gravity" to 25
So what the code is doing in the repeat forever is making gravity lower and lower, so the object changes Y lower and lower.
But when you make the value Gravity equal 25, the object will change Y by 25 and move up instead and it will bounce up. Then 25 will get smaller and smaller until it is negative because of the Increase Gravity by -1, and when it's negative that's when the object falls down again because then it will start changing Y by a negative number.
Hope this helps and feel free to ask for more clarification