Connect your iPad to your pc and select it in iTunes under devices on the left hand side. Then select the music tab towards the top of the right hand side. Change the options from sync all music to selected music and then select your music in the list you want to sync.
Personally I have a playlist set up just for the iPad and then just sync to only that playlist. This allows me to edit the playlist even when the iPad isn't connected.
Alternatively you can select to manually manage your iPad and then just drag and drop stuff from your library.