A large percentage of Internet users browse the web using their mobile device or tablet.
There are various ways to take your website mobile:
Basic Mobile Site
Just a basic mobile friendly website that is very simple and geared towards a mobile user looking for basic information, a phone number, or directions.
Custom Mobile Site
A custom mobile site is a full fledged website that is built within the size confines of a mobile device. It has all the normal areas of a full website but sized down and built just for mobile.
A responsive design is essentially a website design and build that changes shape and size based on the viewer's device. Responsive designs are becoming increasingly popular as you can build one code base that supports anything from a 4" phone, 7" tablet, 10" tablet, 15" laptop, 24" computer screen, to a 100" tv.
A native app isn't really a website but it's a mobile application that has additional or advanced functionality. This is something that would be built to be distributed through the iTunes app store or google play store.
For more details, take a look at the video we created on the four types of mobile websites.