shared folder vs custom access

Hello, My question is probably so basic it's not even found on the forum. ugh. I am a long time Mac user and understand file sharing, and custom access. I have several network hard drives and manage them ok. I've never been clear on this - I manage Sharing and Permission for any folder using "Custom Access" at the bottom of the "Get Info" window. What do "Locked" and "Shared folder" at the top do that is different? I checked "Shared folder", to see but can't find a specific change to the folder. I've spent too much time over the years for something that didn't seem important enough to create a post. I, finally decided to simply ask. Thanks.