You might read this achievement and go "100, oh geez, I better get going on this one". nah. Even if you specifically don't try to catch them, you'll probably have this by level 9-1. The game is a little generous and makes the pieces "move" a little next to you if you're close.
If you're wondering what the gems and jewlery are just play the first level. When you finish some chains/make a nice combo/beat a level some stuff will fall out of the sky that looks gold. If it lands on your "shooter" you get bonus points.
It's just one of those achievements you'll get while playing without having to think about it, so don't worry about it.