What is ReactJS?
What is React Native?
Starting with the obvious difference, React Native is made for building mobile applications for iOS and Android while ReactJS is for building web applications.
React JS uses HTML in its components since it has a DOM. React Native does NOT use HTML since there is no DOM available on mobile. React Native has equivalent or similar components from the native API that are used in place of HTML tags. For example: instead of using a <p> tag for text, we use a <Text> tag.
In ReactJS, we can use CSS stylesheets. In React Native, there are no CSS stylesheets that we can import and use. With React Native, we use the StyleSheet Object from the native API that has similar (but NOT the same) syntax as CSS to style our mobile applications.
This is not a conclusive list of all the differences between ReactJS and React Native. Play around with both to build the same app and see what differences you can find!