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


then I do it again 100


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

I’m using chrome