It is important that you approach assessment in an honest way and that you only submit assignments that are entirely your own work. Using the work of others without proper acknowledgement is cheating, or unfair practice, as you will have had an unfair advantage in your assessment compared to other students. Plagiarism (submitting the work of others as your own work), self-plagiarism (using your own ideas for multiple assessments), collusion (unauthorised collaboration with other(s)) and exam misconduct (not following rules within the exam venue) would enable you to receive a higher mark or grade than your abilities would otherwise secure.
Properly referencing the work of others is an important skill in higher education, one that you will need to learn. Guidance and tutorials on how to reference in the [the referencing style used by the school] can be found here:
Your subject librarian can also help with your referencing queries.
https://intranet.cardiff.ac.uk/students/your-study/libraries/subject-support/subject-librarians
The University uses a range of different tools and techniques to identify plagiarism and the penalties for students who are caught can be severe. Invigilators are also trained to identify misconduct in examinations. It is up to you to ensure that you don’t commit an unfair practice, whether by accident or by design. It is an offence even when you did not intend to do it.