I’ll try and break it down for you.
Automagic is the new app. It includes visuals (the courses up to now have been audio only). It uses the same content as the courses, but doesn’t cover the whole course yet. You can find some more info about it here AutoMagic Welsh is here! (or by putting ‘automagic’ in the search box)
This forum is more part of the community rather than part of the course, although there are tasks in the course which ask you to post on here. It’s generally for help and encouragement.
Slack is an online platform which enables video chats as well as group discussions. SSiW has 2 groups on Slack - the 6/6 one is for people doing the 6 minute course where you can join video groups for extra help with the course material and practices, and the other is a general welsh Speaking Practice group which anyone (SSiW or not) can access for video meet-ups or chats.
Your subscription covers both the standard course and Automagic as well as membership of the Slack 6/6 group. Use of the Slack WSP group is free (but you’ll need an invite), as is the forum.
The reason there seem to be so many options is to try and cover all the various needs of people learning: the audio course content itself (the ‘old’ course and the newer challenges), visual content for those who can’t manage with the audio-only approach (automagic), somewhere for support (forum), and somewhere to reach other learners face-to-face online (slack), and there is no rigid scheme of how to use them together - basically, they all compliment each other and just offer different opportunities to learn and practise Welsh, so you can use whatever combination works best for you, because what works for you may not be what works for someone else.