7-Zip is a free file compression and encryption tool

It can be used to compress individual files or folders 

Once installed on a computer follow the steps below to compress and encrypt the zip file 

Make sure you know the location of the file or folder you wish to encrypt 

Then click on the start menu and type the number 7 
You should then see 7-Zip File Manager as an option - Click on this 

Navigate to the file/folder you want to encrypt - Select it then click Add (Big green + button) 

It will then give you some options
Change then name if you wish 
Change the archive format to Zip 
Enter a password in both boxes
Change the encryption method to AES-256 
Then click OK 

The zipfile will then be created

This will create a single file with the files/folders in it and require a password to extract them