This is posted in the wrong section (there is an SSD section). However, I'll try to give you a brief explanation of what an SSD is.
SSD's use a different storage technology and HDD's. HDD store everything on a "disk" so to speak, where as SSD's store everything into digital blocks. SSD's have much faster seek and loading times than HDD's, and as such there are many performance benefits to owning one. Benefits include:
- Much faster Windows boot time
- Much more "responsive" feeling of computer - i.e. when you click a program it opens with less lag
- Faster searching, file folder loading, etc.
- Faster loading in games (loading a map, terrain, etc.)
As the first response mentioned, while an SSD can provide significant Windows performance upgrades, the performance difference while gaming isn't as large. This has to do with the way games utilize storage and how whether you have an HDD/SSD will not really influence how well the game plays. The difference could be seen in the time spent loading maps (i.e. in an MMO) or when a lot of terrain has to be loaded at once. However, when it comes to just regular gameplay (like FPS), there isn't much of a difference.