Most web hosts have some type of web-based file management software, but the most common method used to upload files to web sites is FTP (File Transfer Protocol). Once your web host has assigned you an FTP account, you will need an FTP client. Here are a couple of free and open source FTP clients that will make adding files to your web site quick and painless:
FileZilla is a free multi-platform FTP solution. Originally for Windows only, it now runs on Mac OS X, Linux, and many other operating systems. Some of its features include IPv6 support, multiple languages, SSL/TLS and SSH File Transfer Protocol (SFTP) for secure transfers, bookmarks, drag and drop support, keep-alive and many more. FileZilla is free software under the GNU General Public License (GPL).
Cyberduck
Designed specifically for Mac OS X, Cyberduck is an FTP and SFTP client and also interfaces with WebDAV and Amazon S3. It features bookmarking, drag and drop transfer, previewing of files, cut and paste transfer, integration with text editors, and many language translations. Cyberduck is free software under the GNU General Public License (GPL).