Power Qs from a newbie

Apologies for what are probably silly Qs covered countless times before however I have tried to find the answers myself, though google and also forums on here (seeing various power, battery and fridge topics inc on the page below).

After both enjoying caravan holidays in our own youths and as a family ourselves in a large frame tent we decided to get our own and are going away for our first trip.

We purchased an Adria Altea 542DK and have discovered most answers to initial Qs but still have a few i would appreciate help with:-

(1) How do I switch between battery and main power (or is it automatic?) There is what i assume to be an isolation switch (pictured below if I have added link correctly) however the internal lights work with in switched either way, without any external power added so what does this switch do?
(2) How do I charge the battery (if/when needed) - does it do this automatically when towing/plugged into mains or should there be a selector switch somewhere? (as some advice/guides suggest)
(3) I was looking for a panel with battery levels and some other info (such as a charging selector maybe?) but all I can find is the image below - I'm assuming the switch on the left (Volts) is to show the battery level and this looks good as it shows around 13 when I switch it - do I leave the switch off and just switch it on briefly to check the levels, or do I need to leave it on in use as a kind of master power switch? I know the switch on the right is for the water pump (and assume I leave that on when in use, perhaps turning off overnight)
(4) Advice online suggests leaving the fridge plugged in the day before going to allow it to cool down on mains power rather the draining the battery on start up - I have turned it on and left a can in there to see if it gets cold but is there a way to know its on? It doesn't seem to have any LED or similar (its a Thetford N80) - i have turned the selector from off (0) to the mains powers symbol (battery and gas symbols also available).

Thank you in advance for any advice - I'm sure someone here will know all of this and be able to easily advice, for which I will be grateful. I am working my way through a Haynes Caravanning handbook as well as online advice but thought asking here would be more focused.