You have to have the discs to get R3 cranked up for the first time; only the R3 updates are available on the Download page. However, you can download the R6.5.1 free demo right now: https://www.propellerheads.se/download/reason/
and get well versed in R6.5. You can’t open any files you save with the demo, but you can open all of the Demo Songs and analyze them and then work with the devices to do what you learn. That’s about a 6 weeks job in itself (OK, kidding just a bit maybe)
I take it that you bought R3 in order to get the R6.5 upgrade for $169, so forget about using R3 if you plan to go to R6.5. Since you have to wait for the R3 disc anyway, start digging some clams and get the $169 bucks in the next 5-6 weeks to get 6.5.1. You’ll be glad you did, and the R3 disc will make a nice coaster for the coffee table.