Give credit where credit is due. By properly citing the sources you use in your writings, you are both identifying the resources that you used to complete your work and you are formally acknowledging the authors or creators of those resources.
To know more about citation and plagarism, please enroll and take the online course - Information Literacy Training: Academic Honesty prepared by TELI and the Libraries. By watching the videos and attempting the quizzes after the videos, you will have better ideas on how to do citation correctly and how to avoid plagarism in your works.
More information on plagarism is available here.