Adding a subject line to a message makes it a lot more scannable for everyone else. To do that, first you need to expand your compose box by clicking format icon. From there, just type the subject line you want in the first line of your expanded compose box.
An error occurred while saving the commentAdam Steineke commented
It would be helpful if the creator could go back and edit their post to include a subject!
if you have an existing post that you want to show in a different channel, you can edit the message and cross-post. This will add the top-level post to the different channel, but will not include the full set of replies. We will keep this request in mind as we evolve the cross-posting feature in the future and update if the status changes.
Details on cross posting can be found here: https://support.office.com/article/cross-post-a-channel-conversation-in-teams-9c1252a3-67ef-498e-a7c1-dd7147b3d295.