When you write a hub, usually a comment capsule is included. If you want to comment on someone else's hub, just scroll down to the bottom of the hub and leave a sincere comment after reading the hub. I noticed that you've not written a hub yet. I can't help but wonder if you mean how do you write a hub. If so, begin with "start a new hub," then follow the instructions. If you're lost after that, contact me and I'll walk you through it.