I briefly looked at the TestKing site, and I can tell you right away that whoever wrote it is not
a native English speaker.
I'll just say this: caveat emptor.
You can very, very easily be promised a fast-n-easy way to "pass a test," and the people who are pitching these things know that you are probably young,
fairly-recently out of school, and that "school" is a place where "passing the test" is the only thing that matters. If you "pass the test," someone writes the letter "A" on your Report Card, which is "good." If you do not, they write the letter "F," which is "bad." As you know, it doesn't really matter whether you learned
The "real world out there" is n-o-t
so simple. Companies invest in computers to do something profitable with them, and your job, if you maintain those computers, is to keep them up-and-running all the time. This, like, say, "swimming," is something that you can't just read a book to learn how to do. It is a craft.
Be an apprentice.
You need to get inside
the company, so that you can work alongside other people who are doing the work and learn from them
exactly what this
company needs done. There's no "golden ticket" that will get you there. My first job was, literally, to tear paper off a printer and shove it through the appropriate slot. (There were no PCs yet.) I was happy, because I was on that
side of the wall, and I've been "on that side of the wall" ever since.
Be humble, listen more than you speak, read books like crazy, and try not to screw anything up. Acknowledge freely that you don't know much yet,
since everyone starts the same way. Soon, you will realize that you do
know more than you did. You find that, when presented with a
... you either know what to do, or know how to find out. And that's what companies want to buy.