How do animated films get shown on TV?

First you make an animatic demo, which is basically a self-produced ,crude , short version of your idea with far fewer drawn cells, but with a complete audio track. This is then shown to the network(s) and based on the strength of it, they may finance a pilot. For examples you can look at, most animated TV series on DVD include the original animatics that were shown to network execs. I know Family Guy season 1 and Sealab 2021 season 1 have them.