someone, person
者 centers on a person or agent: someone who does or is something. It marks the subject of an action or state, like a person or individual.
person
patient
reporter; journalist
trader; dealer; businessperson; company; vendor; supplier; manufacturer; maker; contractor
young person; youngster; young people; (the) youth
beginner
scholar; academic; scientist
doctor; physician
creator (of a work); author; writer; artist; composer; playwright; dramatist
reader
dead person; (the) deceased; (the) dead; casualties
author (usu. of a particular book); writer
the latter; the second
hero; the brave; man of valour (valor)
believer; adherent; devotee; follower
who; what kind of person
ninja; person trained in ninjutsu and employed for covert purposes in feudal Japan
third party; third person; outsider; disinterested person
person concerned; interested party; related party
actor; actress
pair; the two; both persons; both things
the former; the first
another person; others
dentist
The origin of 者 is uncertain. It may have originally depicted a person or a marker, but the modern form combines 耂 (old) and 日 (sun/day) without a clear historical link to the meaning 'person'.
The top 耂 looks like an old person, and the bottom 日 is the sun. Imagine an old person standing under the sun—someone you can see clearly. 者 is that someone, a person.
For シャ, picture a person wearing a shawl (シャ) standing in the sun. The shawl helps you remember the reading シャ for this person kanji.