“Who” is a pronoun used as a subject to refer to people. “That” is a pronoun used for things or groups. When used as an object, “who” becomes “whom.”
John is the person who brought in the kolaches today. (not “that”)
These are the kolaches that John brought.
This is the team that ate all the kolaches. (not “who” because it is a group)
These were not the people whom John intended to feed. (not “who” — it is an object)
What is a kolache, you ask? (pronounced coal-AH-chee)
Kolaches are Czechoslovakian pastries with a big glob of sweet fruit or cheese on top or with meat and/or cheese rolled up in it. These are popular in Texas, which has a sizeable Czech population. Of course, we Texans like to put jalapeños in our meat and cheese kolaches. Now I’ve got a big hankerin’ for some – and I bet y’all do, too!