Yes, that really is confusing and difficult. And no, you do not have to use these fillers/modal particles. However, since they are often used to make a statement or a request (as in your example) sound less like an order, you may want to be extra careful to always use the polite form (conditional). E.g., in the example you quote, you could just use a question, e.g. "Würdest/Könntest Du (bitte) den Salat waschen?"
And I'm sure that eventually you will have heard these particles so often, in so many different sentences, that you will just know how to use them :)
Does that help?