Learning a foreign language is not a matter of reading some grammar rules and memorizing some vocabulary words-- although those are important activities, not to be ignored. Acquiring a language is learning a skill, not a body of information. It's as much like learning to swim or ride a bike as it is like learning about the Revolutionary War. That is, you must not only understand the ideas and concepts, have information at hand, but you must also make your body accustomed to using that information in physical activity: in this case the physical activity involved is speaking, listening, writing and reading.
You need, then, not only to memorize and understand, but also to practice!
Here are a few brief suggestions on effective practice/study techniques. See your instructor if you have questions, or need help in developing an effective study technique.
If you study by reading silently, you draw only upon your visual memory.
If you study out loud, you double your efficiency by adding auditory memory and you make your mouth work, helping with pronunciation and speech.
Augment your learning potential even further by writing what you have read and spoken.
Instructors usually present and test new language skills in a somewhat segmented, chapter-by-chapter approach, as a matter of administrative convenience. However, actual learning is not segmented at all, but cumulative. You add new information and skills to the old without superseding them. Your instructor will incorporate `old' information and vocabulary in the presentation of new skills; you will benefit from doing the same thing when you study. (For example, practice new grammar concepts with familiar vocabulary, we well as with new words.)
If you are prepared to goof from time to time, or even frequently, you'll feel much less restraint in practicing and trying to speak.