Drop planets to combine them. If they go over the limit, you lose and they explode!
If you want to reset, then create a black hole (which also forms after you combine two suns). However, if you use this ability it will half your points and it only works once a game so choose when to use it carefully.
To get extra points, try to chain multiple planet combinations together to get a combo bonus.There’s a total of 4 abilities at your disposal. Another example, is the lightning, which destroys any planet it strikes.