I see that you purchased RealPlayer 18 Plus, which is the latest version of the product and the only version for which we offer support and updates.
To be able to access the Plus features (such as ''burn DVD''), you need to be signed in with the respective credentials (i.e.your account email address and your password). You can sign out and sign back in -- here's how to proceed: https://customer.real.com/hc/en-us/articles/204040653
Note: To learn how to check if you are signed in, please consult the following article: https://customer.real.com/hc/en-us/articles/204040723
For more information on how to burn DVDs, please click on the following link: https://customer.real.com/hc/en-us/articles/204041013