How to access my HestiaPi from outside my house

You will need a WiFi router with port forwarding feature (most routers do these days) and if you don’t have a static IP (or if you don’t know what this is), you will need to use a free Dynamic DNS service called NoIP. Don’t worry – although we can’t offer support on individual routers, we can certainly point you in the right direction. Installation instructions on the above link.
Alternatively you can use my.openhab.org which is a service hosted externally and is not controlled by us or you but by OpenHAB itself. Go to http://[YOUR-HESTIAPI-IP]:8080/paperui and select Add-ons > MISC and install “openHAB Cloud Connector”. Once installed SSH into your HestiaPi (username: pi and password: hestia) and type:
cat /var/lib/openhab2/uuid
write the output down. Then type:
cat /var/lib/openhab2/openhabcloud/secret
write this output down too.
Then go to https://myopenhab.org and create an account using your details and the above information (UUID and secret). You can now access your HestiaPi Touch from a browser or your mobile app (enter “https://myopenhab.org” as a remote url and your myopenHAB account username and password as credentials). The above steps are also available in youtube format here too.