Do you mean before you start playing? In that case just... tell them about it. This will depend on your players' tolerance for reading, but I personally have a discord channel on my group's server where I put all worldbuilding I want my players can to have access to. Mine is in the form of threads each about a single topic (this or that country, how magic works, the politics of how magic works, dragons, etc), but really anything goes as long as it's easily accessible. Then tag the ones you think are necessary as required reading.