I ask a question on Google, then it gives me sites which don’t have anything to do with the original question. This is all to do with my Mac?
Google has gotten less useful for everyone lately. Apparently Google is not keeping up with the SEO spammers and their new keyword spamming techniques. A poll on Lifehacker (http://lifehacker.com/5730396/over-77-percent-of-lifehacker-readers-say-googles-search-results-are-less-useful-lately) has shown that an overwhelming majority of users think that Google has become less useful. It's not just you and it has nothing to do with your Mac.
do the results not relate to your question at all, i.e. not even to single keywords within your question?
You might not be searching Google using the right techniques. Have a look at this article for some guidance: http://www.makeuseof.com/tag/master-the-google-search-like-a-god-save-time/
Or you might be dealing with Malware on your computer. Highly unlikely on a Mac, but not impossible. Check out this article for anti malware software recommendations for the Mac: http://fruitgeek.wordpress.com/2010/06/03/best-free-antivirus/
We could help you a lot better, if you gave us a sample search you're doing and the first couple of results you receive. A screenshot would do. Also specify on which subsidiary of Google, e.g. Google.com or Google.it you're performing your search.
Let us know and we'll try to provide you with the best solution!