How it is determined how much content is shown on featured slider?

What determines how much (and the format) of the text that displays over the featured images on the main page? It seems to only grab about 3 words for the very last line, and I wondered why. Thanks!

WordPress by default for Excerpts uses first 55 words and cuts the rest. However, you can adjust it by adding your Excerpts manually. Manually added excerpts won’t get cut.

There is a special field called Excerpts under Post Edit screen. If you can’t see this area you can enable it via Screen Options on the upper right corner.