Standard Import means that a full copy is made of the sound being imported, and that copy is put into Director's cast as a sound cast member. Therefore, the original sound that is outside of Director can be moved or deleted, if you wish (though it might be good to keep it in a folder named "original media for this project").
Link to External File for large sounds (over a MB):
Link to External File means that the sound being imported shows up in Director's cast, and can be used much like a Standard Import sound file, but the actual sound data is being stored in the original sound file (which is outside the actual movie).
This means that you need to plan ahead before importing the sound. Before you import the sound, it is best to have your movie saved in the same folder as the sound (makes everything easier later).
The original sound that you imported, which is still sitting outside of Director, CANNOT be moved or deleted or else the sound will cease to work in Director. This is because Director has linked a space in its cast to the original sound sitting outside of the Director movie. If you move the Director movie somewhere, you must also move the externally-linked sound file to the same place.
If you try to play 2 different sounds in the same sound channel at the same time, they will either cut each other off, OR the last one you try to play will cut off the other one.
If you try to play 2 different sounds in 2 different sound channels at the same time, they will both play at the same time. This means you could easily play 8 different sounds at the same time, with one sound playing per sound channel.
From the button at the top left of the Library Palette window, choose Media > Sound. This should display the 6 sound behaviors available in Director 8.5
Play Sound, Pause Sound, and Stop Sound can each be dragged onto a sprite or into the scripting channel (meaning you can put these behaviors onto sprites or onto frames as needed). To make them work appropriately, you just need to have your sounds already imported into the cast, and you need to choose the desired event to trigger the script.
For example, if you want a sound to play when you click sprite 1, you wouldn't drag Play Sound onto a frame, you'd drag it onto sprite 1, and choose the mouseUp event. Remember which sound channel you chose to play the sound in (you could write it down).
When using lingo behaviors to play sounds, be aware that if the sounds are long or looped the sound will continue to play to the end (or forever, if looped) UNLESS you use Lingo to stop the sound (or unless you play another sound in the same sound channel, which will cut off the earlier sound and play the new one).
To control sounds effectively, you need to remember which sound channels are playing which sounds, and you need to use the corresponding sound channel numbers for the sounds you want to affect.
For example, say you used Play Sound to play a sound in sound channel 5 when you click on sprite 1. If you later need to stop that sound, you'd have to remember that it is playing in sound channel 5, and use that channel number appropriately in a Stop Sound behavior (on either a frame or a sprite) to stop the sound.