I just bought a netbook. What should I use to protect it from bad computer stuff?

I recently got a netbook and I want to get some spyware, malware, and virus, protection and also cleaners for other things that might junk it up.
On my desktop I have CC Cleaner, AVG antivirus, Advanced System Care and Malwarebytes’. I’m wondering if those programs might be too big for my netbook and really slow it down or make it not function as it should.
I have a Acer 10.1” Netbook PC, with # Intel Atom N550 processor
1.5GHz, 667MHz Front Side Bus, 1MB L2 Cache, 2GB DDR3 SDRAM system memory, # 320GB SATA hard drive, Windows 7 Home Premium 64-bit Edition. It also came with the Nook e-reader installed. I am just running the McAfee trial security that came on it.
Does anyone have any suggestions on what I should do to protect this little netbook. I bought it for travel/portability, and it’s not my main computer, but I do want to keep it running smoothly and trouble-free.
I am not at all computer literate, so if you could please use simple terms to help me get my cute little netbook protected.