I make account but now how can I add my website files

I have my website files saved in usb

Vercel will need to find your repository from some cloud git provider like Github, bitbucket, azure dev ops.

You'd have to create account on something like github, upload the code, then add it to your project on Vercel

If you don't want to set up a cloud git provider, you can use Vercel's APIs and send a POST request containing all the files to your project, got some docs here: https://vercel.com/docs/deployments/overview#vercel-rest-api