When to prune an apple tree

[RJUKL]

I have a young apple tree which is two years old and very spindly. It is a Jonagold and I must not miss the opportunity to prune it this year. Am I right in thinking it must be pruned in the winter and when is the best month?

[Hawkwalk]

between December and February is best, while the tree is dormant.

[RJUKL]

Thank you