I have a question, that I know was answered by a specific user, but I can't find it via a general search. Can I narrow my search to that user's responses? If not, please make it so.
user:USERID to your search, replacing USERID with their actual user id. View more advanced search options at https://meta.stackoverflow.com/search.
user:4228 is:answer how
You type this in the search box of Stack Overflow or Stack Exchange.
The results will show the answers from user 4228 (or whichever user ID you want) which has "how" as a word in it. This is an example of keyword searching. You can remove the keyword and it will show all their answers, eg: