Hi,
I’m Md. Ohiduzzaman. I’m new in programming. Currently, I’ve learned basics JavaScript as my first programming language. My expertise in HTML5 and CSS3 is intermediate level. Now I want to learn ReactJs. Do I need to be an expert in JavaScript to learn ReactJs?
** My English is not good. Sorry about that. I hope you understand, what I am trying to say.
You certainly need some familiarity, but for sure you don’t have to be an “expert”.
My suggestion would be to head over to the official React documentation and do the tutorial to see if you can follow it or you are lacking some understanding 
There’s even a Prerequisite section 
You can find it here
No. But React’s API is very small, it doesn’t really have anything that isn’t just JS (even JSX is just function calls dressed up to look like HTML). So knowing JS well is helpful. However the reverse is also true (in that, because it is almost all just JS, it should help make you better at that)
I suggest first to learn Node.js (for backend) and later choose any frontend framework.
(you can find fresh Nodejs tutorial in udemy)
Node is pretty useful but programming a server application involves very different set of knowledge to learning a frontend GUI framework: different purposes, different patterns, different techniques, different coding styles. Not saying it’s not useful to know, and if OP wants to go into server-side development rather than frontend, definitely, but there’s a big gap between the two things – they happen to use the same language, but they don’t really overlap a huge amount.
I would say what @DanCouper said is accurate. If you have a decent understanding of JS, learning React will help you learn it better. Also, going with something like Gatsby will help you learn JS and React even better, as it really simplifies a lot of the concepts and makes them accessible. I would recommend the GatsbyJS Tutorial.