Lentils come in a few different colors, as far as I know there is little
nutritional or other difference between them.
Basic word of advice: never pre-soak lentils, they cook very quickly and
don't need pre-soaking of any kind.
Here's a quick recipe for using them.
Cube a medium potato, dice a carrot and about 1/2 an onion, mince one or two
cloves of garlic. Take all, put into a 2 quart pot, add about a cup of
lentils (any color will do), add water to cover, bring to a boil. Then
simmer for 30 minutes. Makes a great lunch dish!
If you like, add some curry.