You need to forward the correct port on your home router - 80 for http, 443 for https, 22 for SSH - to the internal IP of your OpenMediaVault.
The most secure way to do it is not to to forward the service port itself, but to forward a high number port e.g. 54321 to port 80, 54320 to port 443, 54319 to port 22. So when you are outside your home network you would connect to your home public IP on whichever of those high number ports you want - i.e.
http://myipaddress:54321,
https://myipaddress:54320, ssh via putty or similar on port 54319. It just helps prevent the bad guys pummelling your OpenMediaVault device with logon attempts. Make sure you change the default password on the device. 12 characters at least - length trumps complexity.
If you tell us the model of your home router we can probably give more specific instructions.