One of the most important aspects of academic writing is making use of the ideas of other people. This is important as you need to show that you have understood the materials and that you can use their ideas and findings in your own way. In fact, this is an essential skill for every student. Spack (1988, p. 42) has pointed out that the most important skill a student can engage in is "the complex activity to write from other texts", which is "a major part of their academic experience." It is very important when you do this to make sure you use your own words, unless you are quoting. You must make it clear when the words or ideas that you are using are your own and when they are taken from another writer. You must not use another person's words or ideas as if they were your own: this is Plagiarism and plagiarism is regarded as a very serious offence.
The object of academic writing is for you to say something for yourself using the ideas of the subject, for you to present ideas you have learned in your own way. You can do this by reporting the works of others in your own words. You can either paraphrase if you want to keep the length the same, summarise if you want to make the text shorter or synthesise if you need to use information from several sources. In all cases you need to acknowledge other people's work.