PuTTY is a terminal program for the Windows platform supporting the secure shell (SSH) protocol to establish a secure connection and provides access to the Ubuntu Linux console command-line. It is open source software and free to use.
You find the latest version to download PuTTY here: https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html
To access your server, be it your home server or a cloud instance, you will need the IP address of the target system and the login information like user name and password or a key file with your private SSH key.
On the server side, SSH server needs to be active and the applicable port (the standard port for SSH is port 22) needs to be open for communication.
While PuTTY is a tool to provide access to the command line, you may also want to install WinSCP on your Windows machine. WinSCP is the tool of choice to easily transfer files from the Windows system to a server or vice versa: WinSCP to transfer files between Windows and Linux using FTP and SFTP