Not sure exactly what you are asking. There are several errors on
your diagram though
You have missed the id off events_services unless that is actually
showing a habtm between events and services
Why has service got an event_id?
You either need a belongs_to between service and tender and the associated id.
You have info_id instead of info_type_id in info.
You have habtm between user and conversation_user and that and
Conversation where I guess you mean has_many/belongs to.
I can't believe you both those relationships between user and
conversation, it appears that a conversation is linked to users via
two paths which is probably wrong.
All in all the whole thing is too complex for a starting point,
particularly for a beginner. Pick a section of the problem, model
that and develop it using TDD. Then add some more.