First you download Tweener Class from here:

Than you unzip the archive and copy it to your project folder.

Than you import it in where you need to use it:
import caurina.transitions.Tweener;

And than you use it, example:
mc.alpha = 0;
Tweener.addTween(mc, {alpha:1, time:1});

First I set the alpha of ‘mc’ MovieClip to 0, than I added a tween, a tween that will fade in my movieclip in 1 second.

Complete documentation of Tweener:

See how to create a MovieClip by Action Script 3: