Man! As much as you did say you don't have a development background, which also contradicts that you are planning to build a React Native app, I hate comparison questions like this one. The only two common thing in between them are they are for web development and they work with DOM but other than that apples and oranges. Bootstrap is like Gijo Varghese mentioned mainly a css framework. I can't even call it a framework. some mixins and helper classes to make your UI look nicer with less effort. Comes with predefined responsive classes, color schemes etc. so instead of styling your entire application from scratch you just use their class names in your elements or extend them with your needs. Also not everything can be done with pure css. it comes with some most common useful javascript components to make it more useful ( tooltips, sliders, affix, tabs, modal, popovers etc )
on the other hand there is React. In spite of most people call it a framework, it is a Javascript library for building UIs (ref. reactjs.com) a framework is much more complicated and complex structures i.e Laravel, Spring, .net etc. It uses a shadow-dom to render components in the background when props/state changes and applies changed parts on visible DOM, and does it very fast. You can find a lot more about their technology and techniques in their website.