help to identify the problems with a 2 year old apple tree

Please help me to identify the problem with my 2 year old apple tree. I am very inexperienced gardener, so any help will be much appreciated.

It looks like some insect colony.I have attached the three photos which I hope will help you to identify the problem. I would be extremely grateful if any of the more experienced gardeners would advice me on the best way to solve this.

It looks like you have a mixture of aphids there. Pick off any curled-up leaves and then spray with a food-safe insecticide from your garden centre. You will need to wet the actual insects on the underside of the leaves for it to work - it will probably need two or three applications.

Thanks very much. I will  try what you suggested.