Here is a lot of information on how to use the RinexLab and what you can expect from it. The RinexLab is an online GNSS post-processing service using PPP, PPK and VRS algorithms.
Do you need to calculate the coordinates of your GNSS receiver? Then PPP or PPK will be useful to you. You do mobile mapping and the management of GNSS base stations is restrictive? Make your life easier with the VRS service