How words are created
By imitation of sounds (onomatopoeia)
Meow, bang, crackle, zip, ring
Through extended meanings
The verb fly becomes: the name of an insect, a baseball that is hit high, the space over a theater stage
From study comes student, from moon comes month
Through compound words
Notebook, bedroom and mailbox are some obvious examples but also note elbow (ell + bow) and lackadaisical (from the expression 'lackaday' which itself derives from 'alack the day').
From root + affix
Prefix + root
Pro- (forward or forth) + duce (lead) = produce ("bring forth")
Root + suffix
Wonder + -full = wonderful
Through changing pronunciation
Breakfast, cupboard, extraordinary
Through changing spelling
Alone is from 'all one'. Felt was once used to strain liquid, so the piece of felt used as the strainer became known as a felter, which later changed to filter. "God be with you" was once a valediction which, over the centuries, came to be pronounced and spelled as good-bye.
From names (eponyms)
The Teddy Bear is named after Teddy Roosevelt and the electrical volt after Alessandro Volta.
Frankfurters after named after Frankfurt, Germany, and jeans after Genoa, Italy.
Kleenex, Band-aid, Jello, Xerox, Hoover
From the shortening or truncating of words
Telephone becomes phone, photograph becomes photo, megabyte becomes meg
Sonar = SOund NAvigation Ranging, laser = Light Amplification by Stimulated Emission of Radiation
Motor + hotel = motel
From foreign words
Influenza (Italian), rendezvous (French), chow (Chinese), opal (Sanskrit)