Guys no problem in helping the poor guy, at least he is willing to get in the gym and get his shit sorted, which already deserves a helping hand even if it is spoonfeeding him to get him started. Everybody has to start somewhere and a lot of those posts have contradictory points usually since it's not written for same body types.
Mozzie you have a belly that you want to get rid of so I will tell you the same I tell my MMA students and cardio clients, your body wants situps...and a lot of them. Doing sets of 20x4 won't get you there this era. You have to train yourself to do 100 situps continually at a go and you have to do that exercise twice a day if possible, as soon as you get up and just before you go to bed. You said you had a guy already training you so he might give you the same advice or something in that line.
Diet is 80% unfortunately if not more, so you will have to feed your muscles growing while cutting the fat. Out of the 168 hours in the week, usually only 4 or 5 are exercising, the other 163 hours are spent on recovery. So training basically makes up 3% of your regime

...the other 97% is eating properly and recovery. Since you have never exercised really you are privileged since you now can properly shock your muscles for maximum growth. You need to feed them. You must stay away from sugary carbs as you belly will be the place it goes. Stick to complex carbs. You need a good whey protein and weight management shake, not mass gainers as they contain mostly sugars, usually 75% or more that will once again go to your belly. The weight manager is balanced between carbs and protein. Then a creatine will really go a long way to boost your muscle gains, give you energy in the gym to lift more and help with recovery. I do not know what your budget looks like so you will have to clarify that point. Shakes I would recommend is either LION premium whey or SSN whey and then Evox 5XL Muscle Meal for the weight manager.
Here is my recommendation for your body type which seems to be a hardgainer:
As soon as you get up in the morning you need to feed your muscles and body as they are starved through the night. Food won't do it since it takes too long to get absorbed and usually lacks amino acids to absorb properly anyway. So you take your 5XL shake. between 2-3 hours later you have a breakfast meal, something with complex carbs and protein. 2-3 hours later you have another meal once again with complex carbs and protein. Doesn't really matter what foods you mix to get those nutrients, as long as you get them. Check the package labelling to get a idea what food contains. Keep this pattern of eating. A hour before you go to the gym drink your Creatine if you bought and 15min later drink another 5XL shake. You need the quick release carbs to sustain you in your training session. Directly after training you have your serving Whey Protein to get muscle recovery and repair going. Since the 5XL is basically a liquid "meal", try to place it in the timeframe of a meal. Also note you have to get at least 3 solid food meals in through the day and 2 inbetween 5XL shakes otherwise it might overwhelm the stomach. Shakes are not meal replacements and never will be, they only supplement your current already-well-planned diet. DJ might help you out in the meal combinations if you are struggling, he is always willing to help.
How many times do you train per week and how do you train? A guy might train for 13 years and be an expert in his own body type but may not be so well versed in knowledge in another person's body type. Do some research on training, it will enlarge your own knowledge base a lot.