It's important to cite sources because:
What is a citation manager?
Citation managers are programs that allow the users to collect, organize, and cite sources. They also allow for collaboration and some provide the ability to store and annotate PDFs within the system.
Why use a citation manager?
Get Started with Citation Managers
Zotero is a free, open source citation manager with a desktop app, browser extension, and integration with Google Docs, Microsoft Word, and LibreOffice. Check out the library's Zotero Handout.