Your session will be automatically detected when you kill a ranked boss. If you had the boss in range from the beginning to the end, application will upload your session to the server and you will be informed about it. Additionally, you will get a link to the saved session. If for some reason the session is not uploaded to the server, you will also be notified about it with an adequate message.
Ranked DPS is calculated by dividing the damage dealt by the duration of the session. The moment of aggro boss is considered the beginning of the session, the end of the session is his death. The session length is the same for each participant in the raid, no matter when they joined it. Therefore, the ranking DPS on the website and the DPS calculated in the application based on the period of particular player's activity may differ from each other.
Q: Why I am getting this message: 'PvE session from boss couldn't be uploaded. Session is incomplete'?
A: You have registered less damage than boss has HP. It can be because you weren't in range all the time or boss got reseted and didn't regenerated to full HP.
Q: Why website shows lower DPS than app?
A: DPS in app is calculated for each player, taking the time between first and last hit on chosen target. On the other hand ranked DPS on website is calculate based on the duration of the entire session, from the moment of taking boss aggro till its death.