Cookies are small text files that help organise and store browsing information. They are not programmes, and cannot damage your computer or any files you have on it, nor can they transmit viruses.
The cookies I have on my site don't collect any personal information or anything which can identify you as an individual. They don't add you to a mailing list nor do they enable me to contact you after your visit.
Find out more about cookies in general here.
My cookies help the site work better. They also help me know how many people visit my site, which pages they go onto, and whether they are first-time or returning visitors. Knowing how people use the site helps me to provide more of the content you want to see.
I also occasionally embed some links or content from other websites such as paypal. These are clearly identified, but as a result you may be presented with cookies from these other sites. I cannot control the dissemination or operation of these cookies and you should check with the websites they come from for more information about them.
Bear in mind that if you do not accept cookies, some parts of this (and other) sites may not work as planned, or sometimes may not work at all.
If you still prefer not to accept cookies the easiest option is to set your browser to block them. http://www.aboutcookies.org will help you to do this if you don't know how.