To find fairly detailed info:
- Press Windows Logo Key + R (at the same time)
- Type MSInfo32 into the box and hit OK.
- Select Summary on the right for a summary of your system.
You can also select other items on left, for example clicking on Components then Storage then Drives will give you a list of all drives including their capacity and free space where appropriate.
There are 3rd party utilities on the market that will provide even more detail if thats what you need.
If you know the make and model no. of your PC you could go to the PC manufacturer's website and look for the specs. there.