It's possible your computer already has one built in, but if not, there are a number of good, free, SSH tools out there.
If you're using Mac OSX
Find the 'Terminal' application and type the following at the command prompt:
If you're using Linux
Run the same command from your own commandline.
If you're using Windows
You may need to download a free SSH client. We recommend Putty. It's free and lightweight. Just enter your server hostname, ensure that port 22 (SSH) is selected, and connect. You'll be prompted for your username and password.