A Shade is where black or a colors opposite color on the color wheel (complimentary) is added to make the color go darker.  

Why not just add black?

A lot of artists feel by adding a colors opposite on the color wheel, gives more interesting and lively darks. You don't ever need to get a black if you use this method as you will be able to make any black (reddish, greenish or bluish ones) you need. A purest may say different.. to each his own.

A Tint is the addition of an opaque White to a color.

A tip to making the lightest tint ..

If you are wanting to make the lightest tint of a color, you should consider starting with the White paint first and add the smallest dot of the color..
You will be surprised how little is needed to color the white.

some topics following on from this you
might want to check out.

• making a Color Wheel
• the 8 colors you'll ever need