In some cases, you might want to use more than one domain name for your Podpage. Maybe you own both www.myawesomeshow.com and www.myawesomeshowpodcast.com and you want people to visit either one to end up at your Podpage. That's totally possible.
The biggest thing to know is you need to pick one to be your main domain. It's HORRIBLE for search engine optimization to have two domain names with the same content. Therefore, you need to decide what your main domain name is going to be. Maybe for the example above, you want your main domain to be www.myawesomeshow.com.
Here's how to get both domains working with Podpage:
Follow the instructions and get your DNS Settings working with Podpage
Once your main domain is working
Sign into the site that you bought your secondary domain from (GoDaddy, Google Domains, etc...)
Select the secondary domain name and find "Forwarding"
Forward the secondary domain name to the primary domain name.
If there are settings for "Forward with path" and "Use SSL", select both to true
If there are settings "with masking", turn that off
This will make it so anytime someone goes to your secondary domain, they'll be sent to your primary. This will be much easier for everyone (including Google)