Learn Turkish: Pulu zarfa yapıştırmak için bekledim. - I waited to stick the stamp on the envelope.

This is how Turkish expresses purpose. By combining a dictionary-form verb (like yapıştırmak) with için, you create the meaning 'in order to stick' or just 'to stick'.

Why is it pulu instead of just pul?

The verb yapıştırmak (to stick) needs a direct object because you are sticking a specific item. Adding the accusative case suffix -u to pul shows that 'the stamp' is the specific thing being stuck.

Why does zarf (envelope) have an -a at the end?

The -a is the dative case suffix, which acts like 'to' or 'onto'. In Turkish, you stick something 'to' a destination. Since the envelope is the target where the stamp goes, it becomes zarfa.

Why does bekledim (I waited) come at the very end?

Turkish puts the main verb at the end of the sentence. The entire phrase pulu zarfa yapıştırmak için acts as the reason why you waited, so that whole block of information comes before the main action bekledim.