You posted in the OS 10.3 (pre year 2000) forum instead of the iPod forum. To get answers to your question, next time post in the proper forum. See https://discussions.apple.com/index.jspa I'll request that Apple relocate your post.
If you use automatic syncing, select the iPod in iTunes. Toward the top, there is a bar of buttons, staring with Summary. Click on Music next to Summary. This is the iPod's Music screen, where you tell iTunes how to sync songs to the iPod.
If you are currently using automatic syncing, the check box for Sync Music should already be checked. That setting turns ON automatic syncing. (If it's not currently checked, you are not currently using automatic syncing.) Choose the option to sync Select playlists, artists, albums, and genres. Below that, there are lists for choosing what you want synced to the iPod. Under Playlists, the playlists in your iTunes library are shown. Select (checkmark) the ones you want on the iPod.
When you click Apply, the iPod's existing content is replaced by the content you selected on the iPod's Music screen. So, if you selected playlists, the iPod will only have the songs on those playlists after syncing, along with the playlists themselves that you can use for playback (on the iPod). Going forward, any changes you make (adding and/or removing songs) to those playlists (in your iTunes library) are synced to the iPod automatically, the next time it is connected (or click Sync if already connected).
NOTE: You are not the original topic poster. In the future, it would be best to create your own forum topic to ask your question. You can do so going to the appropriate forum category. For example (for this question), you would go here and click on the type of iPod you own
On the forum category page, click on Start a discussion, under Actions.