Critical =/= criticism. Critically analysing something doesn't mean criticising it in the colloquial use of the term, it means using critical thinking in evaluating it.
For your other question, just focus on what you got out of the reading/experience, rather than just listing that you did it. So instead of writing "I read X and it was interesting", explain why it was interesting, what led you to read it, how that integrated into what else you have read or knew, etc. Basically show how that experience has developed your perspective through your writing (i.e. how your writing about that has fundamentally changed now you have read and know X).
It's kind of hard to explain without examples and I'm hard pressed to think of one offhand, particularly as I'm not really sure what you're applying to.
The only one I can come up with is an example from my recent PS (for applying to ancient languages) - I wrote about how I audited a module in a particular ancient language, then discussed examples of how that language compared and contrasted with another I had studied and related that to some reading I had done on a proto-language that they are both considered to have derived from. Rather than just saying "I should study ancient languages because I audited this module on an ancient language and found it interesting", I tried to show how that experience developed my understanding overall while (hopefully? I got an offer so...!) demonstrating the kinds of skills needed for that course.
Obviously the specific content isn't relevant for a science course in your case, but hopefully that illustrates the different approach.