motivation to work out

So recently I moved in with my grandma... And she cooks hearty cause, well...she's a grandma. So I've been gaining some weight. So tonight I found this pretty cool workout app that seems okay. I did the first days workout. But I just really need to stay consistent. I am very skinny but I don't want to lose weight... I just want to tone my body. So how do I find he motivation to work out every day ?