“Good morning guys, how is everyone doing today?”
“Hey guys, what’s up?”
These would be some common greetings to a group of people, but not necessarily only men.
“Guy” is a casual expression for “man” and is used quite often.
“Who’s the new guy in accounting? He looks smart.”
The female counterpart is “gal”, but that expression isn’t very common anymore. It sounds old fashioned and quaint, something I expect to hear in a movie from the 1940s or 50s. “Guys and gals” sounds very old fashioned.
When you address a group of people of mixed gender you could say “Ladies and gentlemen” but that is very formal.
“Good morning ladies and gentlemen, and welcome to our fundraiser”
In non-formal situations you can use “everyone” or “everybody” when addressing a large group.
“Good morning everyone, ready to start today’s lesson?”
But sometimes you are talking to a small group, or you want to sound casual and friendly. So even though it is not proper grammar you will often hear people just call a mixed group “guys”.
“Good morning guys, how is everyone doing today?” could be a boss talking to employees, or a teacher talking to students in a causal way.
“Hey guys, what’s up?” could be you meeting a small group of friends, that is either all male, or mixed gender.
However the singular word “guy” still only refers to a man.