In our example phrase, ”kauppias hoitaa homman,” hoitaa appears in the 3rd person singular. Note that for this verb, 3rd person singular is the same as the infinitive form. (See hoitaa fully conjugated here.)
”Kauppias is a noun that means ”shopkeeper.” It comes from kauppa (”shop”), and appears here in nominative singular.
Homman is the genitive singular of homma which means ”the job” or ”the work.” In the genitive it means ”of the job.”
Our whole phrase translates as ”The shopkeeper takes care of the job.”
The nouns hoitaja (”caretaker,” ”caregiver” or ”nurse”) and hoito (”care”, ”treatment”) come from hoitaa.