(In the english language)
You might want to start by browsing web sites on etymology:
These sites reveal that English words are created in many ways. The
word might come from another language, whether classical like Latin or
current like Spanish. The word might be derived from an existing
word, or a combination of two existing words. The word might simply
be made up. And there are other possible origins as well.
Here is a handy chart, describing ways in which words are created in
"Etymological Theory: How Words Are Created"
Take Our Word For It
If you are wondering about how words, once created, actually enter the
English language, here is an article on this subject. The article is
from a British perspective, but I suspect that an American perspective
would be similar.
"How Words Enter the Language", by Michael Quinion, 13 July 2002
World Wide Words
Search terms used on Google:
"how are words created"