Tug meaning is used when you want to show ownership, like Qhov ntawd koj yog kuv tug. Or it classify a noun such as "Tsis muaj ib tug neeg tsis nyiam". Tus is used as an article like "Tus me nyuam, tus noog." It can also be used as an adjective like "Daim av no nyob tus tus."
For uas and ua, uas is used to clarify who such as "Tus uas nyob ntawd". Ua is to do like "Koj puas ua li cas?"
I hope this clarifies it a little, sometimes Hmong can be hard because words are so closely related in sound, spelling, and sometime meaning.