i just recently found a unknown computer in my workgroup,I am not sure what a "workgroup" is but I am the only user as my computer is for personal use only, so why am I seeing someone else my workgroup and do I need it?
All XP and above PCs belong to a workgroup, default name is MShome.
A workgroup is the name of a "group" your PC belongs to - it is always looking for deices that have the same workgroup name. This is different from a domain (normaly used by companies)
other devices on your workgroup may include, mobile phones connected to the PC, other PCs connected to your router, wireless devices connected to router, PCs that friends had plugged in but have now been removed.
If you're sure the other device is a PC maybe worth looking into, worse case, someone stealing wifi