since you are the owner/creator I doubt you need to do this. You can set permissions to pswd protect it. If you share the puter and want to keep imp. confidential stuff in there, (such as passwords or pron), you don't want anyone to see there are apps to encrypt it and it has to be unencrypted using a pswd you make.
get a program like winzip. once that is installed then go to the folder you want to password and right click select and add to zip file then in the window that opos up very bottom left hand side is a button named password click that and give it a password you remember
Depends on the structure of the password, I use at least 8 -10 letters. I have also tried a word, 6 letters and random letters and symbols. Using L0phat4 the word was cracked in a cpl. of minutes, random letters took longer but was cracked, random letters and symbols took the longest, several hours but was also eventually cracked. In my opinion 8-10 letters is okay to use for a home puter assuming the sharer isn't very savvy and doesn't have L0phat4 at their disposal.
Ep, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS