Almost all works are covered by copyright, wherever they are found and even if the author has not explicitly claimed copyright. This restricts copying such works. However certain exceptions can be used by students. The main exception that a student might rely on to make copies is doing so for non-commercial research and private study. Nevertheless, this doesn't give a right to make as many copies or as large copies as you would like. You would have to limit copying to a fair dealing amount. And any works you use in an essay or presentation should always be given full accreditation.
Use your library resources to access materials. These have been bought specifically for your academic research. And always credit the authors by using your school's recommended referencing style. You can find comprehensive guidance on the relevant school page of the library website and by accessing Cite Them Right in the online resources.
The concept called fair dealing allows for reasonable use of copyrighted materials by individuals, providing they fall within the following guidelines:
According to the Intellectual Property Office this means that any use that undermines a publisher's sales are not permitted. However, limiting your copying to one chapter from a book or 10% of the book, or one article from a journal would normally be considered to be a fair dealing amount.