Remember the SHARE tab is for how things are "shared" over the network. The security tab is for how things are shared over the network AND locally.
If share permissions conflict with security permissions for a network user, the most restrictive permission will apply to the user.
Shares can get VERY confusing when you have multiple accounts on the same machine and you want to make certain folders "private" locally but still have network access to them. Even more so if only certain people have accounts on certain machines. Things would be slightly different in a domain environment.
Example: I have a folder called "XXX" and I don't want my spouse to have access to that folder! She, by default has access to ALL folders outside of "My Documents". I suppose I could just put the "XXX" folder inside a subdirectory of "My Documents" but I also want my brother to have access to the "XXX" folder.
So what I am looking for is, allowing my brother and myself access to that folder over the network and locally, while denying my wife access to that same folder. Since we all have local accounts, by default we all have access to the "XXX" folder, what I need to do is set up sharing with security.
I would do the following, on the SHARE tab I would give me and my brother full control and my wife DENY. This takes care of NETWORK permissions ONLY. I would then go to the security tab and add my wife with DENY permissions, this takes care of things locally!!!
This is a very basic tutorial, other things to keep in mind is that if my wife insists on admin rights on her account then all bets are off. At that point she could just take ownership of the folder and game over!!! (Thank God for Domains!!!)