React to express consfusion(help needed)


im abit confused with connecting react to express, i feel like this is the last step in the process of me just creating a register page. the user just has to register.i am connected to mongodb atlas, my backend code works fine as i tested it in insomnia. react app form registration works fine but i am abit confused to how react connects with express, i need to know if react is connected to express properly(this is part of a project to apply for an internship)
should i create another page in frontend or put in any other code?
i just feel like im missing something very small.
let me know to include other info as well
please see attached images of my code below: