Please, let some nice and patient person explain me what tool do I need and why?
I use React and I will use Redux and also Rlectron and semantic-ui library which needs gulp.
So my question is: Do I need webpack? What is the main difference and how to deal with it?
You won't need gulp
for what you described. webpack will serve you well. Also, react-semantic-ui has a react binding so you don't need extra build steps for that.
Why webpack? It's a much safer choice at this moment for bundling and building a react app.