Literary criticism, according to the Oxford English Dictionary is the 'practice of judging and commenting on the qualities and character of a literary work'; by this, in your role as a someone studying English Literature, you are already a literary critic by proxy. When teachers and exam boards talk about the involvement of criticism and criticial outlooks in your coursework and exam responses, they are asking you to situate your own analysis, or criticism, in relationship to somebody else's. You are being asked to take part in a pre-exisiting debate on what the meaning of the literary text is.
To do this efficiently you must first understand what pre-existing readings of a text there are: go away and read some books, some journals, articles or essays and watch some documentaries to scope out what people have been saying about what a text means previously from a simply literary perspective or from psychological, philosophical or political points of view. Next you should make consider how you feel about these analyses, do you agree with them? Do they need to be explored further? Or do you disagree with them? In your essays and exams you should seek to use critical evidence in relation to your own analysis and use it to showcase where you own new ideas have advanced from and insert your own ideas on what the text means. At the moment, a lot of criticism might feel very alien to you but it's okay to feel confused by some critics' ideas - take the time to find the background behind their thinking on websites that are easier to proccess before advancing onto the jucier criticism. Just remember - you're a critic too!