how to logout of NAS folders on from File Explorer

[greengoat]

Hi,  I am very new to using a NAS.  I would like to know how to logout of my NAS from my Windows File Explorer?  I am concerned after I access my files that someone can come right behind me and go in my folders from my desktop or if someone gets into my computer.  There is no way to logout of the NAS. (at least I do not know how)  I do not know if there is something in the control panel that I can check off or what.  I used to could just shut my computer down and when I started the computer back up; I would have to login to the NAS to access the folders.  Now if I shut the computer down I do not have to log in.  I can go right to Network,  click on my NAS name,  and there are my folders.  This is not safe.  Can someone help me find a better  and secure way to use my NAS.  I want to be able to get to my folders from my desktop and then log in and out of my NAS whenever I want to get access to my folders or even add items into my folders.  I am asking because I do not know any other way to go about this.  Can some help me please? 

Thank you in advance for your help.