You can't directly add to a collection set.
You can add to a collection in the collection set, and then the photo also can be found by clicking on the collection set.
i believe you mean publish to a photo hosting service rather than a collection?
if so go to Library view, select your photo service in the left hand vertical menu and go through the set up process. It is very intuitive.
Once set up select the photos that you want to publish so you can see them in the bottom ribbon, as if you were going to review them.
click on the thumbnail that you want to publish and drag it to the photo service (Pixiset), and let go. It should go into the photo stream for that service. Continue until all of the photos you want to publish are dragged into the Pixiset photo stream. click on that photo stream then click publish ( just below it). Sit back and wait until the photos are published.
As an alternative to using the thumbnails to click and drag you. An click and drag the image displayed in the main viewing window.
Hope that helps.
Thank you so much for taking the time to answer my question!!!!!!
no problem at all, that's what these forums are for
if you liked my answer please click the question as answered thank you.
Enjoy LR, publishing becomes addictive!