"I quickly go there into the restaurant and eat lunch."
Translation:Odaugrom abba az étterembe és ebédelek.
as the hover over says, it means "into that" coming from the determinative "az" and affix "-ba", simplified to "abba" to ease pronunciation. It is used to specify that particular restaurant. With "abba" the Hungarian sentence means: "I quickly go into that restaurant and eat lunch (and none else)" without it, the sentence is also correct, but means "I quickly go into the restaurant and eat lunch"