React Express

JSX is an extension to JavaScript that adds a new kind of expression. You can use JSX expressions anywhere you could use any other expression.
JSX is a shortcut for using the React.createElement() API, that is much more concise, easy to read, and visually looks a little like the generated UI (as both are tree-like). You don't have to use JSX, but there are practically no disadvantages, so you probably should use it.
JSX is tag-based like XML. Each tag, like <div />, is transformed into a call to React.createElement(). Any attributes become props of the instantiated component. Attributes can be strings like foo='hello', or they can be interpolated JavaScript expressions when wrapped in curly braces as in bar={baz} (which would set the bar prop to the variable baz).
Tags can be self-closing, like <div />, or they can include both an opening and closing tag, like <div></div>. To include children elements, you will need to use an opening and closing tag and put the children tags within.