This allows you to add an extra bit of pizzazz. I recommend adding anything like this (rhinestones, studs, etc.) with a wet q tip. This can be fun but may not be for everyone.
For nail art, you will need a variety of colors. Any Sally Hansen (or other brand) will work for this. Just make sure you have the colors picked for your design first.
The top coat I use, but again, any will do. This makes nail polish appear shinier for a longer amount of time, seals in the design, prevents chipping, and may help polish dry depending upon the formula