from experience, most functionally illiterate people will know a few key words, can perhaps read numbers, and know how to sign their own name. What they can't do is scan a document for relevant information nor can they read a passage of text and gain information from it. They can maybe recite the alphabet, maybe. They can also sometimes sound out certain words if they really, desperately need to get through some text.

Almost all of them I've known have worked in manual or household labor type jobs. A few have done pretty well for themselves actually. One of my students worked as an HVAC installer. A lot of the time they'll have kids or a spouse who knows how to read as well. Almost all of them I've known have had miserable lives, shuffled around living from one relative to another, long periods of homelessness, losing custody of multiple kids, never making above minimum wage. It's hard for them to do basic things and yeah, they're often very reliant on family or close friends.

A guy I went to high school with is functionally illiterate and will admit it. He owns a tire shop in my hometown through sheer happenstance and lives in a mcmansion. America is a silly place.