I don't know that this is really "basics" in a sense, but I'm a bit stuck. At the end of every BJJ class, we roll a little bit. Typically, I'll partner up with someone and we'll start on our knees (so as not to give any person an advantage or having any oversized takedowns). My problem is nothing we've covered in class involves both people being on their knees. As such, I have no idea what to do, and (being reactively minded in the rolling) I find myself getting submitted without even being mounted (or getting a shot to go into a guard). In other words, from the knees, my partner will manage to put me in a guillotine or somehow pull off a kimura, leaving me in want of an actual technique to use... instead resorting to an ugly survival mindset.
This survival instinct you talk of is the basis for any grappler starting out
Until you have a decent amount of experience and you're rolling with way better guys, you want to be setting yourself goals like 'don't get tapped by this guy'. That way you build up a stellar sub defense. Meanwhile at the classes you'll be learning attacks and you can start feeding them in once you are confident and have stopped getting tapped out every minute.
As to starting off, you can pull guard or go for a takedown depending on what you're comfortable with. I usually prefer to pull guard because I like sweeping and can usually end up in a much better position than if I were to go for a takedown.