After finishing the base game quest "Tending the Flames", the player can speak to Valerine. One of the dialogue options the player will have is "I've interest in the spoken word!".
This will prompt Valerine to offer to teach the player the skills of an Emissary. If the player accepts, they will be given a brief tutorial on how the system works, and walk through a few example dialogue choices.
After the player completes the training example(s), a new dialogue option will become available, "Have you any Emissary work for me?".
Valerine sends the player on a mission to speak with a Solitude Guard named Norlund, and convince him to be an informant to Valerine.
Norlund can be found near the entrance to Solitude, generally leaning against the main wall to the left of the exit gate.
Norlund will tell the player he is busy and ask them what they want. The Emissary options will show up straight from the get-go.
Norlund is most receptive to Heartening options.
If the player fails to convince him, they can return to Valerine for another shot at it. She'll suggest they can bribe Norlund for another go.
When they speak to Norlund again, they'll be able to offer "amends" in the form of 50 gold to have another go.
If they fail again, reporting to Valerine will have the option of letting her take over. The next quest will then not be available until later (a miscellaneous objective will remind the player to check in with Valerine).
If the player succeeded, they can return to Valerine for a reward of 100 gold, and the quest will complete.
The next Emissary job will be available immediately if the player speaks to her again now and asks if she has additional work.