Create an "On-The-Go" playlist
of the songs you want to share on the source iPod. To add a song to this playlist, press and hold the center button on your iPod while the song title is selected. The song title will flash signifying that it has successfully been added to your "On-The-Go" play list. (Note, on 4th Generation Nano you must choose "Add to On-The-Go" after you hold the button down) Repeat this step for all of the songs you would like to include. You can also add entire playlists (or albums, artists, genres) at a time by highlighting the playlist (or album or artist or genre) name, and then holding down the center button.
For more detailed instructions, read this short article from About.com on How To Make An On-The-Go Playlist On Your iPod
Turn on your miShare by sliding the switch to the music setting (all the way to the right) and connect the source iPod to the left-hand (source) side of your miShare.
Wait until miShare's arrow on the left-hand (source) is steady green, and then connect the target iPod to the right-hand (target) side of your miShare.
When miShare's arrows & center button are green, press miShare's only button.
Sharing is done when miShare is blinking green - remove the iPods & enjoy!
in Extras->Notes). Here are some links to Apple's documentation that will help you get the most out of your miShare: