PuTTY is a free SSH, SCP, and SFTP client for Windows. More information about using SSH can be found in the SSH User Guide.
PuTTY also includes PuTTYgen and Pagent, which allow you to generate and manage SSH keys, which is covered in the SSH User Guide - Using SSH Keys (Windows).
PuTTY is available for download here - http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html. Download the A Windows installer for everything except PuTTYtel dot exe file.