Questions from an astronomy hobbyist

After watching the excellent BBC series The Planets, I realized that I know little to nothing about how we actually get rockets off the ground and into space in order for them to explore our solar system. That is probably the case for most people; they're content just to watch the marvel of space travel without understanding it. And I agree--it is wondrous to watch rockets take off, escape the pull of gravity, move into orbit around the earth, and even to watch booster rockets return to their launch pads as was the case with one of the SpaceX missions in 2019 (https://youtu.be/HVqWEoyiaBA). I haven't experienced the need to understand some of what is actually going on, until now. Because I have so many questions; you can't watch programs like The Planets and not have questions. For example, why are planets round in shape, rather than rectangular or octagonal? The answer is gravity. If you want the full answer, google this question and read some of the links that are returned. As it turns out, gravity is the answer to many of the questions about what has gone on and what goes on in the solar system--e.g. the formation of the planets. So what is gravity? My husband smiles when I ask this question; he studied biophysics in college and has a good background in math and physics. There is no simple answer. He reminds me that astronomers and scientists have been studying gravity forever, and will probably still be studying it a century from now. As Wikipedia states:
Attempts to develop a theory of gravity consistent with quantum mechanics, a quantum gravity theory, which would allow gravity to be united in a common mathematical framework (a theory of everything) with the other three fundamental interactions of physics, are a current area of research. 

So, for those of you who understand much more than I do in this field, you'll have to pardon my ignorance. These are my questions listed below, and I'm well on my way to reading about each of them, albeit, reading the articles about them written for lay people. My understanding of the complicated math and physics necessary to understand all of this ended when I was in my second year of college (I hit the math wall when we began to study the derivatives of trigonometric functions). So my interest in astronomy and cosmology is purely that of a hobbyist.

• What are the different kinds of rockets?
• What powers a booster rocket?
• What powers main engine rockets?
• Where are booster and main rockets manufactured?
• Where is the fuel manufactured?
• There is solid fuel and liquid fuel--which ones are used in the different types of rockets?
• Why are nuclear reactors not used to power rockets?
• What keeps rockets going in deep space; why don't they use up their fuel quickly?
• Why do spaceships go into orbit? To save fuel? 
• How did the SpaceX booster rockets manage to get back to earth? Most of the time the booster rockets end up in the oceans and are retrieved by ships for reuse at future launches.
• What is a gravitational slingshot (gravity assist)?
• What is tidal force? (this played a huge role in the formation of the planets)

These are just some of the questions I have, and am currently exploring online in order to find answers that I can understand as a layperson. NASA itself has a very good website that provides a lot of useful information: https://www.nasa.gov/ , and there are other very good websites for astronomy hobbysists as well. 

After seeing the movie Interstellar in 2014, my interest in our universe really took off, if for no other reason than that I wanted to understand some of the concepts brought up in that movie (tesseracts, for example). I bought the book The Science of Interstellar, written by Kip Thorne, and read it carefully. But prior to that, my interest was already piqued by many of the astronomy lectures sponsored by the University of Oslo's Science Library when I worked there as a consultant from 2010 to 2013. There was and is a healthy interest in astronomy and cosmology on this campus, and it was reflected in the choice of invited speakers. And if I think back even further, to when I was a pre-teenager and a teenager, I was already interested in science fiction, reading authors like Ray Bradbury, Madeleine L' Engle, Isaac Asimov, C.S. Lewis, Ira Levin, and others. So the table was set many years ago. At least I know how I am going to use some of my time when I retire; I plan on visiting Cape Canaveral in Florida again (this time I'll appreciate it more), as well as at least one of the astronomical observatories in the USA as well as one here in Norway (not far from Oslo). As one of my former university professors wrote to me recently, 'you'll definitely have no problem keeping yourself intellectually occupied'. I think he's right.