Start by installing it! ;)
BSD is very similar to Linux, just that some programs will use slightly different syntax.
So, if you know Linux, you know (probably 90% of) BSD. :)
You may find some hardware is not supported, so check their compatibility first, or just experiment.
Each flavour of BSD is slightly different, but very similar.
I now use OpenBSD, but I first tried it using FreeBSD, be warned though, they all expect you to read documentation. :)
Jump in & get your feet wet.