Dataplicity is a remote terminal for your Pi. It offers functionality similar to SSH, but it doesn't need any complex set-up to get it working behind firewalls and NAT.
You should ABSOLUTELY change the password of your raspberry pi (if you have not done so already):
First enter your email address, press start and copy the code you received into your terminal.
After Dataplicity has been installed you will receive a link to access your Raspberry Pi.
Now you should first confirm your email and create a password.
Now you can log into your pi account in your dataplicity terminal to have full access to your raspberry pi.
You now have the option to create a wormhole to run a website on your raspberry pi, but that's a topic for another guide.