afew apple trees are self-fertile and will set some fruit,but most will need another tree in the same group near by.

'Near by' can mean in a neighbour's garden (unless you have several acres!)

yes Andrewr is right,neighbour's garden is fine,what apple tree have you got and we can tell you if you need a partner for it or not.

You can look up pollinators on the internet. If you know the name of the tree you are growing. My small trees are being annoying this year. The apples have decided to take a rest this year, but the one that has not blossomed ever is smothered in buds. How it is to be pollinated I know not!! So you can't win!!! Grow pears .....as they are not so fidgety as apple trees with fruiting each year. They need pollinators too.

thanks for all of your answers,much apprichiated. my tree by the way is a cox's orange pippen.