Summer analyst background check & employment verification

Hey everyone, I know there are a lot of threads on this but I was just wondering if we could get a walkthrough of the background check process for summer analyst roles, specifically with regards to the employment verification itself. I know that a 3rd party verification company is used by most banks but I am still confused about how the checks work!

Does the 3rd party verification company pull employment information and details from the resume submitted to your bank OR do you input the details into the 3rd party verification company's portal?

If someone could walk through the process and the specific ways in which the 3rd party company verify, that would be great. Just want to be prepared for the process whenever it starts!

Thanks in advance.