A carrier board which is also called as base board is generally used in tandem with a System on Module (SOM). You need a carrier board for your SOM because it contains the various multimedia and connectivity interfaces that you require like USB, UART, HDMI, etc. Toradex is a leading manufacturer of carrier boards. Get one of the off-the-shelf carrier boards offered by Toradex or get a carrier board which is totally customized to your liking. Check out the page for more details.