This is an easy one to learn once you know one basic fact about the sentence.
Use who when the person is *doing* the action.
Example: I know a friend who will always help other people.
The "who" is the one who will do the helping.
Use whom when the person is receiving the action.
Example: They are the sad people whom nobody helped.
The "whom" are those who did not receive help from others.
Try writing a few sentences of your own with each one and soon you will understand it and never have any trouble with it again.
Here are two sample sentences to try on your own. Place who or whom in the space.
- Anyone __________ the coronavirus has attacked needs to get help soon.
- The best place to go if the coronavirus attacks you is someone _________
has experience treating it.