Sugarcube html help

I am very new to this! I am learning to html little by little, I am starting to play html games and cheat to get more money or stats. But some times it doesn’t work I get NaN or I get the number I want but nothings happens and when I do it again the number doubles. Like

SugarCube.State.variables.money+=100

100

then I do it again

SugarCube.State.variables.money+= 100

200

I’m still new so if you explain like I’m a 5 year old lol

I’m using chrome