Messaging
Starting a conversation, what the composer does, attachments, and the one-thread rule.
Messaging is part of Premium. A free account can open the composer and will meet the price at Send.
One conversation per person
You and a given freelancer have exactly one conversation, for ever, whatever brought you together. Applying to a second job of yours moves that conversation's context rather than starting a new one.
The alternative was a list where two rows read "Maria" and nothing on screen could tell you which was which.
Starting one
"Message" on a profile, on a card, or from an applicant. There is nothing to set up: the thread is found or created and you are in it.
Writing
Bold, italics, underline, strikethrough and both kinds of list. There is no link syntax and there never will be