As postage is formed by two complete words, post age, so is a compound word.
The unstressed syllable in the word "postage" is "ta".
The postage stamp on the envelope was colorful.
I don't seem to have enough change for postage.
No, building is not a compound word.
The contraction (not a compound word) is doesn't.
Upwards is a compound word.
The affix is "-age" in "postage". It is used to form a noun. Other examples of words ending in "-age" are shrinkage, usage, spoilage, and leverage.
2
There is no compound word.A compound word is a word like bus-stop.Husban is spelt like this husband
Upstairs is a compound word, so it is one word.
It cannot be a compound word.
Mango is not a compound word.