Running surface

Hi, I am aiming to complete my first FLM next year and I am training for the GNR in September. I am very new to running having only completed a 5km so far. My last training run was for 45mins running on the pavement. At the end of the run, my back and knees were very sore.
I am a bit confused about the running surface. All the pavements I have been running on are tarmac. The roads are a mixture of tarmac and stones. Every article I have read tells me not to run on concrete (meaning roads and pavements).
Does this mean I can't train on tarmac roads and pavements. Won't the GNR and the FLM both be run on the road? So doesn't this mean I should train for the surface I will be running on?

Concrete and pavements are the hardest surfaces of all. Tarmac (nice black stuff) is a little more forgiving.

If you can do as much of your training as possible on a variety of surfaces and particularly off road, this will reduce your chance of injury.
When you train for an event such as a marathon the commonest injuries are overuse injuries which is caused by the relentless pounding on hard surfaces. You won't be able to do all your training off road, and your long runs will probably be all road, but off road will also strengthen your ankles etc.

Re the pain in your knees and back, are your shoes worn out, maybe you need a more cushioned pair suitable for high mileage.

Good Luck