SermonSpeaker is free to use. However it's nice if you want to give something back.
There are various ways how you could contribute to the SermonSpeaker project.
Translate
Creating new language files for SermonSpeaker or improve an existing translation is probably the best way to contribute to the SermonSpeaker project.
Translating SermonSpeaker is done with Crowdin. Crowdin is a webbased localization platform which makes it quite easy for translaters and developers to work together. Just join a language and start translating and voting.
Layout
While I think I can write software quite good, I'm horrible at everything related to design and graphics. So if you can create a better layout than what is included in SermonSpeaker, feel free to share it with other users. That's another very good way to give something back to SermonSpeaker. Look at the articles about layouting to see how custom layouts can be built.
Create Graphics
As said I'm not a graphics guy. Thanks to Almuth Lauch, I got a nice logo.
However there may be other graphics within SermonSpeaker which could use an improvement. If you're good with graphics, you will see the possible improvements better than I do for sure :)
Rate
Rating SermonSpeaker on the Joomla Extension Directory (JED) helps get SermonSpeaker used more. Especially if the rating is good.
Report
If you think you found a bug, feel free to post your findings in the forums. This is the best way to get me notified.
Code
If you are able to provide the code to fix a bug or even created a new feature, you are welcome to share this code with me. The easiest way to do this is by using GitHub. Just create a PullRequest with your proposed changes and I will probably merge it. Read more in this article: SermonSpeaker & GitHub.
Donate
At the bottom of each page is a "Donate" button. This allows you to donate some money using PayPal. This is by no means required to use SermonSpeaker, SermonSpeaker is completely free to use without any fee. But if you feel like supporting me financially, this is the way to do it.