I am drafting a response to your questions, but also want to know why you are being so analytical of this sort of thing: 1. To be able to explain this to your mom? 2. To strengthen your English grammar knowledge for school? 3. To develop a strong English grammar base to use as a foundation for Spanish grammar? 4. Are you thinking of becoming an English/Spanish teacher? The reason I ask is that as a native speaker of English, you are bound to use these structures in an organic matter in a normal conversation, that is, the right structure will come to you as needed without analyzing it. However, if any of the above points apply, then you need to understand some basics about 1. Parts of speech 2. Sentence structure 3. Types of sentences 4. Verb form/tense before you understand the intricacies of syntax and semantics. It is difficult to explain the differences of the verb forms you are wanting to understand without having some basic knowledge of the above.