Everyone has a Missal and silently prays the Mass with the priest. The Missal is in Latin and English, and I read everything in English before Mass so I can read it in Latin during Mass. The altar boys say the responses.
IHS, which you see when the vestments are laid out, is a monogram or symbol for the name Jesus. The letters are a contraction of the Greek word for Jesus, which in Greek is spelled IHΣΟΥΣ.
A genuflection is made every time one passes the tabernacle out of respect for Christ within.
There is a good linguistic reason for saying Holy Ghost. The name comes from the German, Heilige Geist, which means Holy Ghost.
My warm-up explanation has not been reviewed by anyone else.