Adding a resuming feature to a download manager

Question

Hello,

So i've created my own download manager and after a while, i remembered that i need to add a resuming feature to it. What i mean resuming isn't threading, i have that already. What i want is to be like. Adding the Packets/Sockets to a file, so when the program runs again, it reads the packets so it continues where it stopped. Like pressing a button, makes the application, creates the file and write in it the download data and then exits the application. After launching the application again, makes the application read the file before it starts a new Thread/Download. I've read a lot of things, ThreadPool, and BackgroundWorker. But i didn't understand anything. Would someone tell me how to do it or explain more of it.

Thanks