Automatic Gearbox

Although I passed my driving test in 1968, I have never driven a car with an automatic gearbox, until now.  (Kia Sorento 2.5 Diesel Auto). First time out towing with it and not sure of the best way to get the best mpg, so I just used drive. Any one got any tips for getting the best mpg? What is the best use for the manual bit marked + and -?. I noticed when climbing a hill the engine revs increase but not the speed, why? I have heard that it is better to lock it in 5^th on a motorway, whatever that means, and does using the cruise control give better mpg? Sorry for so many questions but I am travelling to Scotland soon and as it will be mainly all motorway I just wanted to get the best results.