As you may already know Media entity module entered Drupal 8.4 as Media module earlier this year. This was the result of years of hard work in contrib and core space. While the module stayed conceptually the same we used this opportunity to clean it up and refactor some things; mostly to make APIs even easier to understand and use.
Media entity comes with the concept of so-called source plugins (also called type plugins in the past). They are responsible for everything related to a specific media type: they have knowledge about their nature, about the way they should be stored and displayed, they are aware of any business logic related to them, etc.
There were many plugins already available before Drupal core decided to adopt the module and they mostly lived as separate modules in contrib space. Since the API changed a bit during the core transition all this plugins need to be updated. The process is pretty straightforward, but the number of modules that need to be worked on is quite high. This means that we'll need quite some help from the community to do this as fast and as effectively as possible.
Here is where you come in!
Are you interested in contributing but don't know how? Are you looking for a task that is relatively simple but not completely trivial? Then the porting of media source plugins might be a really good entry point for you!
There is a meta issue that is trying to keep the overview over the porting process. You will find the list of modules and their current status in it. In order to get familiar with the changes that were introduced during the core transition you should check the relevant change record. All information that is needed for ports should be available there. If you'd rather work with examples then take a look at Media entity image and Media entity document, which were adopted to core as Image and File source plugins respectively.
When you decided which module deserves your attention check its issue queue. If there is already an issue about the porting get involved there. If there is not create one to let others know that you are working on the port. In any case make sure to add its reference to the meta overview issue. This will help us to keep the general overview over the process.
Have you checked all the resources I mentioned above and you feel that there are still things that are not entirely clear? Come to the #drupal-media channel on IRC. We are hanging out in that channel most of the times. Our weekly meetings happen in the same channel every Wednesday at 14h UTC.