Databases are collections of resources, primarily journal articles, but they can also contain conference papers, videos, eBooks, reports, images and more. Many databases specialise in a specific subject area, so you know when you're searching the database you will find material relevant to your studies.
LinkedIn Learning has a series of online videos about operating systems - you can start with the beginner videos. Find out what you need to install, configure maintain and troubleshoot these systems.
Computing and IT subjects covered are, Programming with Java, C, R, Python, PhP, UX design, designing Apps for iOS and Android, Big Data, Responsive Web design and many more.