Versailles from Paris

Look in any guide book.

You take the RER C commuter train to Versailles Rive Gauche Chateau -- it is roughly 4 Euro each way -- get two tickets for each person. You follow the crowd to the Chateau which is an easy 15 minute walk away. Get reserved entry time slot in advance. There is perimeter bag check and then you jjoin the line for your time slot.

When are you planning to travel? (as in during the Olympics or Paralympics or during a "normal time")

It also can depend on where you are staying. I usually take the RER C line out to Versailles Rive-Gauche station. Here are the specifics from the official Versailles website.

https://en.chateauversailles.fr/plan-your-visit/practical-information#getting-to-the-palace

Agree, read Rick’s guide, it was so easy. We purchased our tickets at the station that morning. We left from the station near the Musee D’Orsay.
If you arrive too early for your time, they are strict about it, there is a self service cafe to the left side of the Palace to the left. If you go to the sit down cafe on the right side (still on the left side of the Palace), take the elevators up - all marked signage.
BUT AN FYI. If you go up the elevators, there are restrooms which were empty both times we used them. Before our time and after our visit.

Strongly recommend the Kings Apartments tour ... it was cheap and you don't have to wait in line (which was insanely long even when we got there super early) - you just go wait in a nice building with seats and restrooms - and you get to go into places that are not mobbed with people. Then after the tour, they let you loose with the masses!