Welcome to Codidact!
This is mostly a Q&A community, as you likely know from Stack Exchange already. However, I only said "mostly", because there are some differences you should know:
Codidact is more community-centered
Community is central to Codidact. In fact, we couldn't exist without communities that want to use our platform. Hence we try to support them as much as we can, while leaving them as much autonomy as possible. Many site features can be customized for communities to provide the best support for their needs.
Furthermore, imposing and enforcing rules is mostly a community business. If a community wants to have strict rules for comments, that's okay. If a community wants relaxed rules, that's okay too. We'll also try to implement features in a way supporting the rules made up by the communities. There are some obvious exceptions, namely our Terms of Service and our lightweight Code of Conduct.
But the community-ness goes much further. The whole software is open-source and can be found on GitHub. We'll eventually found a non-profit organization, which will also have community-elected board seats. There will be a democratically elected and independent review panel for handling appeals against moderator actions and reviewing moderator conduct.
There is more than just Q&A
Codidact started as a Q&A site and is based on a "classical" Q&A software, but there are plans to improve the Q&A format from what we have learned in a decade of using Stack Exchange. Not all of those changes have been implemented yet (as this is a purely volunteer project, time and resources a quite limited in comparison to a commercial platform), but we are working on them and some will be released quite soon.
One thing we want to improve is finding more ways to present useful content. In a classical Q&A site, there are only questions and answers. But for example a Cooking community might want to have a place for users to share recipes. And some sites want to host regular competitions (for example our Writing community).
To mitigate these issues, we have two feature sets in our site:
Categories. Categories are broad top-level separators. By default, every community starts with two – Q&A and Meta –, but it's possible to add more categories for specific use cases (for example: Challenges, Recipes, ...).
More Post Types. Depending on category and site settings, it's not only possible to post questions (with answers), but it's also sometimes possible to post articles (without answers). We also plan to add more content types, for example something like a "Wiki" post, which can be edited by anyone.
Additionally, some changes to comments are currently being planned and designed. The most important change will likely be, that it is possible to define comment threads.
Voting and Privileges work differently
Voting and privileges are also working differently.
As you can see, we show up- and downvotes for posts. This is, because we want to give less focus to the total score (upvotes - downvotes), but rather allow uses to evaluate the votes themselves. (Because +100/-90 means something completely different than +10/-0). In the same manner, we also order answers a bit differently – see this help page if you are interested in the math.
One major change is that we have removed reputation-based privileges and replaced it with something we call "abilities". They are more specific, so that you only get those abilites the system has specifically learned to trust you in: For example if you make continuously good edits, you will be able to edit other people's posts without review. More details can be found in the feature announcement.