"He starts eating."
Translation:Ele começa a comer.
"Ele começa comer" is not accepted. Is this just another one of those "learn which prepositions goes with which words"-situations or an error? :)
Yes. Começar + a. But sometimes you may see this verb not being followed by the preposition A! (Meu dia é assim: começo comendo duas frutas...) it will depend on the context. But he general rule is começar+a