Taberu is a verb that means to eat. Koto is an intangible thing, opposed to mono--a tangible thing. If you put Koto after a verb it then the verb describes Koto. So taberu means to eat, but put Koto after it and you have taberu koto which means "eating" as in "the act of eating". On a more general note, if you put a verb in front of a noun with no particle between then the verb describes the noun. So example Taberu koto ga suki desu I like eating. Wasyoku wo Taberu Koto ga omoshiroi Eating Japanese food is interesting. You can't just put ga after a verb. It would be incorrect. Ga goes after nouns only.

Taberu - eat koto ga - to