Using K2, I want to select the users of whom the K2 items would be shown to.
How do I do this?
So far I have created user groups and put them under registered users.
Are there any components that would allow this?
If you want to control access to K2 articles individually, you can do that inside that article settings in the "Access Level" field. The same setting can be applied (Access Level) to K2 categories inside each category's settings. Most likely, you've got all these set to "Public". In order to create different access levels, go to Users > Access Levels.