US southern slang. Usually preceded or followed by "now."
It means "listen to what I have to say next, because it is something that you were unware of or had previously been ignoring, much to our chagrin."
or can simply mean "look at this."
Now, lookie here: we don't appreciate that kind of foul language here.
Lookie here now: The way you're cutting them switches is all wrong. Use a sweeping motion.
Lookie here! It's a dodo bird!