You can use the build in MS Security Essencials if you want but you are better off with a 3rd part.
I use AVG Free. Have for a very long time. Buying software VS Free ones usually just have extra stuff that most of the time you dont need unless you are paranoid. I know I tired quite a few different AV's with different viruses I had and honestly the only two that had anything slip though them was MS Security Essencials and ESET Nod32 which i use to support a lot until i found out it lets CryptoWall virus, which encrypts all your files and you have to pay to get them back unless you have a backup, though where as everything else caught it.
Doesn't matter if you are running windows 95 to windows 10 you always want AV protection though.