Answer:
Man's most important invention.
Lots of them make up a word, And lots of words are in them. It's easy when you think about it. A while ago we stamped and mailed them.
What is always coming but never arrives?
I start in little but I end in full, you'll find me in half and complete.
What you do to determine the length of something
How did the farmer find his wife?
Easy
Animal
Difficult
Food
Funny
Kids
Logic
What am I?