The grammar explanations on these pages are short and simple. They describe the typical situations in which the particular grammar form is used. As such, they may help you to understand, for example, when the present continuous tense can be used for a repeated event. However, trying to learn the explanations as rules is like trying to learn tennis by reading a book. A much better idea is to look at the many examples for each grammar use. You could then try to memorize some sentences that you have personalized. So, for example, you could change the sentence You're always interrupting me .. to My mother's always telling me to clean my room! You could also be alert to this use of English in your own reading or listening.
Important: The rules on these pages will help you get started in your understanding of English grammar. Please realize, however, that English is very much more complicated than can be explained in a few simple sentences. As you learn more, you will find examples where the simple rules shown here do not apply. Taking note of these exceptions or refinements will help you deepen your understanding of how English works!
If you want a reference work on English grammar, I can thoroughly recommend the following:
Practical English Usage. Swan, M. 1980. Oxford University Press.
Finally, have a look at this cartoon. The message is clear: communication is more important than correct grammar!