A snapshot is a virtual machine that is in a specific state. When working with snapshots, there will still be one virtual machine that can easily be restored to a specific state. The major difference between a clone and a snapshot is that a clone is a new virtual machine that is independent of the original virtual machine. Even if there is some relation between a snapshot and a clone (for instance, you can create a clone based on a snapshot), a clone basically is a new virtual machine. This means that once you have created a clone of a virtual machine, you can even start creating new snapshots of that virtual machine.
When creating clones, you really need to think well about what you want to use them for. If you just want to use them for your own convenience, a linked clone is the best solution. It can be created very fast, and it takes the least possible amount of disk space while it still offers full functionality. The major difference though is that you'll never be able...