How Do I Create an Apple Podcast?
To upload your created Podcasts to Apple you do this direct with iTunes.
Firstly I would recommend reading through the following article on Making a Podcast:
Once you are ready to upload your Podcast open iTunes and sign up for Apple Podcasts for Creators. Then click on Podcasts in the top menu and on the right-hand side at the top you will see a link for 'Submit a Podcast'.
You then enter your Podcast RSS feed and click continue and follow the instructions.
Why Is My Track Listed as Album Only on iTunes?
There are 2 common reasons that your track will be listed as "album only" on iTunes.
The most common is that your track is longer than 10 minutes in length. Any track that is longer than 10 minutes will automatically be listed as "album only" on iTunes.
The second possible reason is that your label already has the track in question for sale on a separate release. If iTunes detect this (which they do not all the time) then they will put the new occurrence of the track as album only and go on the assumption that users searching for the track will buy it off your other release.
As frustrating as this is, unfortunately, nothing can be done to reverse Apple's decision to mark your track as "album only".