These resources are public, free and a great start. Yes I know some of them are just Wikipedia, but it's a good place to start so get on with it :-)
|CPU||Wikipedia||Central processing unit|
|HDD||Wikipedia||Hard disk drive|
|NIC||Wikipedia||Network interface controller|
These online videos expand on or replace the above resources if video is your preferred medium.
|All components||YouTube ("Basics Explained, H3Vtux")||What does what in your computer? Computer parts Explained|
|CPU||YouTube ("In One Lesson")||How a CPU Works|
|RAM||YouTube ("PowerCert Animated Videos")||RAM Explained - Random Access Memory|
|HDD||YouTube ("Basics Explained, H3Vtux")||How Do Hard Drives Work?|
|SSD||YouTube ("Branch Education")||How do SSDs Work? How does your Smartphone store data? Insanely Complex Nanoscopic Structures!|
|NIC||YouTube ("Ace Networker")||NIC (Network Interface Card)|
|GPU||YouTube ("Basics Explained, H3Vtux")||How does a graphics card work? GPUs and Graphics cards explained.|
This isn't required and is probably not a recommended use of your time. It's simply an option.
If you're looking to get certificate in computer hardware then consider the CompTIA A+.