Your site can be uploaded in many ways, but the most popular is FTP.
When your hosting account was created, you were provided with an FTP account. Using software such as CuteFTP or WS_FTP, you can log into your host.
Then, using the program like a normal windows program, you drag and drop files onto your Web host's server. These files become live online instantaneously.
There are other ways to upload your site, including Secure Shell (SSH) or uploading files through your browser.