1. "limdu" is a verb in the past tense, third person plural.
2. "avur" is used with either nouns or pronouns, and when it is used with a pronoun it must be conjugated. We don't use it with verbs (as opposed to "bishvil"). A couple of examples:
.המכתב הזה עבורך This letter is for you.
התשלומים האלה הם עבור החודשים האחרונים These payments are for the last months.
איזו means "which" (female singular) but we often use it also in the sense of "what kind of".
It's במילה because you have the verb "to use - lehishtamesh", which in Hebrew is followed by the preposition "ב":
אני משתמש במחשב. I use a computer.
זו is synonymous with זאת.