When you are ready to program a vehicle, you need to go to the manufacturers website and purchase a subscription. Each one is a little different. Most of them have short term subscriptions of 24-72hrs and costs range from $10 to $100 USD.
Gm recently changed to a licensing by VIN number, so it is $40 for a single VIN but you have programming access to that VIN for 1 year.
Nissan requires the one time purchase of a program AND subscription to program
After purchasing the subscription you should be give a link or access to download the OEM software if you haven't already.
You can go NASTF.org to see a list of OEM reprogramming subscription costs as well as some helpful links and information for each manufacture.
https://www.nastf.org/i4a/pages/index.cfm?pageid=3291
https://www.nastf.org/i4a/pages/index.cfm?pageid=3639
Do your research before you commit to programming via J2534. Some vehicles just aren't worth trying to flash even if they say it's possible, others are very straight forward and reliable.