If you're using Windows, download PuTTY to connect to external servers from their official page, here: https://www.putty.org. Open it after installing it:
Paste your IP address into the Host Name input and connect to it by clicking on Open. It will warn you about connecting to an unknown server; just click Yes. Then, it will ask you to log in; type root as your default username: it's different for each hosting provider.
If you're using Mac, you can simply use the following command instead of using PuTTY:
ssh root@<your-ip>
Although root is the default user provided by DigitalOcean, note that it may be ...