Generally, material can be copied from the internet into an assignment or essay in the same way (and subject to the same “fairness” requirement) as you could copy material from a book.

Note however that, while under copyright law you might be able to copy something into your project, this does not mean that you can pretend that what you have copied is your own work. You must always attribute it as being another person’s work and you must credit the author. Plagiarism (copying other people’s work and pretending it’s yours) is a serious matter that is usually dealt with very severely by educational institutions.