The pronoun "quisque, quidque" is translated 'each one,' or 'each person.' It's used to describe people without specifically identifying them. In English, we use "everyone," for this function. [e.g., "Everyone does it."]
It's declension is based on that of the interrogative pronoun "quis, quid" which you'll study in Chapter 19. The declension is straightforward. The most interesting thing to note is that you use one form "quis" for both masculine and feminine in the singular.