How to study?

So I’m studying for my GED. So the books has chapter and each chapter has lessons and at the end of each lesson there is a test.

So what I do is I read the lesson and then take the test but I failing the test because I don’t understand some words. Should I read the lesson once and take the words I don’t understand and then read again the lesson and then take the test?

And I also don’t understand some words in the test so should I take the time to search for those words as well and then take the test?

Or what’s the best way to do it?

I feel like I’m kinda slow and just wanna finish my GED