In English there are at least two sounds for the letter l. When it occurs before a vowel, we usually pronounce it with the tongue quite relaxed, the tip of the tongue against the hard gum ridge, the sides of the tongue turned down slightly to allow air to pass laterally. To test this, notice the position of the tongue as you are about to say liquid.
Now say all, and you will see that for a final l (and also for l before a consonant, as in milk), the tongue has quite a different position, and the l has a much darker sound. The tip of the tongue is still against the gum ridge, but now there is a deep depression down the center of the tongue, which is arched toward the back of the mouth. The root of the tongue is depressed.
