Woodpeckers use their long, pointed beaks to peck at tree trunks and eat the insects inside.
Literal
Woodpeckers [topic-は], long pointed beak [with-で], tree [gen-の] trunk [obj-を] pecking, inside [to-に] existing insects [obj-を] eat [polite-ます].
きつつき (啄木鳥) 'woodpecker' is written in hiragana here. 尖ったくちばし 'pointed beak' uses the past participle of 尖る 'to be pointed' as a modifier. 幹 (みき) 'trunk' is the tree-specific anatomy term. A clean, informational nature-description sentence suitable for elementary reading practice.