I have used Slimware and it's not bad software, but it is very naggy and started to have some advertising unless you purchased it. It is supposed to update your drivers if needed. I prefer to update my drivers from the manufacturer's website and uninstalled it. I don't know what kind of computer you got, but one of the biggest complaints is the huge amount of "bloatware" that comes pre-installed on them. It's all about money and one of the ways they can sell cheap computers. The first think I do with a new computer for someone is get rid of all of it as it can really slow things down.
As Jenny said, you probably already have a trial version of some kind of anti-virus program. It's very common to have McAfee pre-installed. You will have to pay for it after the trial period. If you like the software, that's fine. I don't care for McAfee myself, but if that's what you have, you may like it, so give it a try.
Also, as Jenny said, whatever you do, don't install something else - having more than one anti-virus running can make an awful mess.