Is there any reference documentation regarding architecture and Flow of Jitsi meet. I wanted to know about the role of Jitsi-Meet, Prosody, Jitsi Video bridge and Jicofo when user joins jitsi meet ?
No, there are no such graphs. You can find a small network diagram here: https://github.com/jitsi/jitsi-meet/blob/master/doc/manual-install.md#network-description
Jitsi-Meet is the web/mobile client. All communication is xmpp(prosody server) and all participants enter a muc room, and jicofo (the conference focus) enters first. Jicofo opens channels by communicating witj jvb and invites the participants to send audio&video to jvb. This is a short description of what happens.