>>10805126The first 3 series are connected, but the main cast are barely aware of how the events of the past have led up to the card game controlled society they live in. The only character's from the previous 2 are Yugi's high school bully Ushio, and both Yugi and Judai making appearances in the Bonds Beyond Time special.
That said, if you're planning on reading the manga version of 5D's, know that every Yugioh spin-off has a completely separate story for their respective manga and anime.