What should I know if I am to watch Fafner Exodus without watching the prequel series and movie? I watched the two first episodes of Fafner Exodus, but it was very confusing, as the story is ongoing. Not much intro.

There were a prequel series, and a movie. What should I know from this prequel material in order to understand Fafner Exodus?
There was a prequel series, an OVA and a movie, and they do all need to be watched (and in that order) to understand Exodus.

Fafner's plot is pretty complicated. You may even need to watch the original series twice to understand it (the first half was done by a different writer and isn't as good, but makes more sense on a second watch).

It's a good series (and Exodus is brilliant so far), but it does require a fair bit of time investment, and the plot isn't for everyone.