Hi
Borate has explained very well a method for fade in and fade out.
Remember that you normally fade out to Black and fade in from Black
So ...For Fade-out....
Click the "Add Blank" tab on the toolbar and select Black for the colour.
Click the "Add" button and your blank black frame will be found in the Image folder of the media list.
Drag and drop this so it follows the last clip you have on the sequence line.
Click the small square with the horizontal lines on it, at the end of your last clip (Set Video Transition) and select "Fade" from the list.
Enter the duration for the fade.
Click OK and a yellow bar will generate at the end of your sequence covering the join between your last clip and the blank black frame.
Play the sequence now and you will see your clip fade out to black.
You can adjust the blank frame length and transition timings to get the effect you want.
For a fade in you can simply add a blank Black frame to the start of the sequence line before your first clip.
Click the box with the lines on it as mentioned above and select "Cross Fade" from the list and then follow the same steps as above
This is not as good as the Opacity method suggested by Borate but it is simpler and probably quicker.
Nat