HelloCustomer my name is Dan.
You do indeed need to free up space on the drive if all you have is 10GB. Mac OS X requires free space to run correctly.
If it runs out of it it could lock up and make life very interesting.
You can find lots of information about your Mac in the System Profiler.
From the Apple menu select 'About this Mac' and then More info.
In the list on the left is where you choose the item you want information on, for your hard drive it will be in the ATA or SATA item depending on how new your system is.
I do suggest getting an external hard drive at least 250GB in size and then format it as Mac OS Extended (Journaled) before putting it in service.
A simple thing to do, all the tools you need are already on your Mac.
This site will help you figure out a lot of the differences between the PC and Mac.
Look about halfway down and enjoy.
When you get the external drive let me know and I will help you get it formatted and files moved to free things up.