These are two (of several) basic principles for creating compound words (“kunmetitaj vortoj”) in Esperanto:

1: Two nouns can be combined to make a new word. For example, rivero + bordo = riverbordo. When that occurs, the second part is the primary one: a bank of a river, not a river of a bank.

When two nouns are combined, the first -o ending can either stay or go. Usually that decision depends on pronunciation. “Skribotablo” is easier than “skribtablo” for many people, although you’ll see both forms.

2: Ordinarily, an adjective isn’t combined with the word it modifies. So “bona tago” doesn’t become “bontago”, and “bela infano” doesn’t become “belinfano”.

When an adjective is combined with a noun, it creates a new word with a new meaning. So “bonveno” (bona + veno) doesn’t mean “a good coming” but “a welcome”. “Belarto” doesn’t mean “beautiful art”, but means “the fine arts”.