Offline marketing means marketing not using the web. This may be in the form of distributing business cards, distributing flyers and posting ads on bulletin boards. Door knocking and telling people about your site is also said to be the best ways to market.
Online marketing means marketing using the web. This may be in the form of putting your site on the bottom of your signature in emails. Forum signatures may help too. Making reviews on Amazon and telling people about yourself is also possible. Yahoo Answer may also be seen as a marketing opportunity. Answer questions that are found on your website and post the source page from your site. Offering special deals on your products on your website and announcing it is a good way to get more customers.
Of course, your offline and online marketing should be consistent with one another. They should compliment each other. All information should be up to date.
One thing I might forget is partnerships. Creating a partnership with another is good thing. This means that you can benefit from each other. This is a thing for those new sites.
These are just examples of marketing I usually use to market a site.