Having a peer review from other designers can be an incredibly valuable perspective!
A Rules Exchange can be best explained as a holiday gift exchange; everyone throws a gift into the pool, gifts are shuffled, and then everyone is assigned a gift. In a similar format, every participant submits their rulebook to a spreadsheet before the event. When the exchange begins, rules are shuffled, and you are assigned another rulebook to review and provide feedback on, you will normally have a week to do this. All participants have access to the whole list of submitted rules, so even though you are assigned to one rulebook, everyone is encouraged but not expected to leave feedback on multiple.
Rule submissions can be at very different levels of polish. Maybe you have just thrown together a prototype and want a second pair of eyes on the rules for a sanity check, or maybe you're about ready to hit the Order Print button on your fancy, graphics-filled rulebook and you just need one last proofread.
Regardless of the polish, we highly recommend that submissions are stored on Google Drive and request that they're in the form of a google doc or PDF with comments enabled.