A slow game will be something slower than the 15+10 recommended for Rapid games. For example, 30+20, 45+45, or even slower. I'd probably say that 30+0 is the shortest time control that I would still count as "slow".
For opening/endgame/strategy review, there should be some pages early on in the study plan that give some advice for what these mean, under the headings "Tasks Explained", "Resources and Alternatives" and "Alternatives". (I've had my study plan for a while so the headings may be slightly different in a more recent plan, but the information should still be there.)
Have a read through those sections, and if you're still unsure let us know and we can give you some more specific advice
Finally "Chess content" refers to reading a blog, watching a YouTube video, checking out a chess streamer live online, etc. Basically just think of it as "Chess study free time" as a reward for finishing all the other tasks 
. I wouldn't worry too much about this one if you can't think of anything specific.
In the intermediate plan: What do you mean with "slow games", "opening/endgame/strategy review" and "chess content"? I don't know what to do.
(What i want to say: What is a slow game? Or chess content, opening/endgame/strategy review?)