how to distinguish "a touch of" and "a little of"?

You need to learn to write complete sentences in English--this "how to distinguish" **** gets tedious.

"How does one distinguish between 'a touch of' and 'a little of?' " for example, or "How do you distinguish . . . "

The question is meaningless without context, however, "a touch of" almost always means a very, very little amount of something, whereas "a little of" is relative to something already specified, or expectations. For example, if you are eating a meal, a serving of noodles might be four ounces (roughly 115 grams), but if you say you want a little of that, you might only be given two ounces (roughly 57 grams). The meaning is relative to the specified quantity.

A touch of is a much more indefinite expression.