Make sure "File Manager" is open. Now click the folder you wish to convert to a zip folder and if it turns blue (as shown below) then it's been selected.
By default the setting should be to compress to a zip folder as my settings below are. However if they're not just click "Zip Archive" to set it to the zip file setting. Press "Compress File(s)" when you're done.
You should then see this message appear if the compression was a success. If so press "Close" when it appears.