Channels for a forum Mobile app

As part of my postgraduate I choose a project to work on Couchbase light and sync gateway.
The project goal is to build a forum app for Iphone and Android.

I would like to understand how can I choose the channel id for sync gateway in this case for the post document store?
I have to say that I am still new in couchbase world and need some help.

here is the forum post document I am thinking to use;
“type”: “post”,
“Topic”:“please help me with your knowledge”,
“DateTime”:"“Mar 13, 2015 9:00:20 PM”"
“about”: {
“PostId”: “post-4fgtyeye561h29033665e853a3dc8bc4c5e78f7a6cf8d55910df230567037tgbr-10”,
“type”: “post”,
“text”:“First Message”,
“DateTime”:"“Mar 12, 2015 3:00:01 AM”"


The guide on channel usage in the Sync Gateway documentation is probably the best place to start - it covers how to define channels using the sync function.

thanks @adamf for the link.
In my case, does it make sense to use the topic of the post (topic id ) as a channel id?