Learn Portuguese (Portugal): O desporto é muito bom.

É comes from the verb ser, which we use for permanent or defining characteristics. Saying O desporto é muito bom means sport in general is a good thing. If you used está, it would imply it is only good temporarily, which sounds strange in this context.

Why is it bom and not bem?

Bom is an adjective meaning "good," and it matches the masculine noun desporto. Bem means "well" and is used to describe actions. Just like in English, you say sport is "good," not sport is "well."

I have seen the word "esporte" for sport. Is desporto different?

They mean exactly the same thing, but desporto is the word used in Portugal. Esporte is the Brazilian Portuguese word. Because you are learning European Portuguese, you will want to stick with desporto.

Since this lesson is about gostar de, how would I use this vocabulary to say "I like sport"?