Patents are grants of property to an inventor. In the United States, this means that the US Patent & Trademark Office (USPTO) legally prevents people who are not the inventor from making, using, offering for sale, or selling a product in the United States. New patents are effective for 20 years. To extend the life of the patent, the inventor must pay maintenance fees to the USPTO.
The USPTO defines 3 kinds of patents:
In order to receive a patent, an invention has to meet 3 criteria:
For more detailed information about patents and their criteria, visit the USPTO's "General information concerning patents" site.
Trademarks are basically seals of authenticity of goods. They protect marks (names, phrases, images, logos, etc.) used to distinguish one kind of product from other kinds. Something can be both trademarked and patented: a trademark prevents others from using a similar mark, logo, or design, but it does not prevent others from making or selling your actual product or service under a different name.
Words, phrases, symbols, designs (or a combination of those things) that distinguish a product or service from other kinds of products and services. The mark has to be unique: it can't look like, sound like, or mean the same thing as an existing mark (if it does, that's called "likelihood of confusion").
Unlike patents, you don't have to apply for a trademark right away: sometimes it takes years to achieve the brand recognition you need to argue that your logo/color/name/etc is distinct enough to be trademarked.
For more detailed information about trademarks and their criteria, consult the USPTO's "Basic Facts about Trademarks" document.