Learn Hardcore Portuguese (Brazil): Esse carro é bom.

Esse generally refers to something close to the person you're speaking to (or something just mentioned). Este often refers to something close to the speaker, and aquele refers to something far from both the speaker and the listener. So in many Brazilian Portuguese contexts, esse is the natural choice when pointing out a car that's near the other person or was just introduced in conversation.

Why is the adjective bom in the masculine form and not boa?

In Portuguese, adjectives must agree with the gender (and number) of the noun. Carro is a masculine noun, so we use the masculine form bom. If the noun were feminine (e.g., casa), the adjective would be boa.

Could we ever use está instead of é?

Yes, but the meaning would change. É comes from the verb ser, used for permanent or lasting qualities. Está comes from the verb estar, used for temporary states or conditions. Saying Esse carro é bom implies a generally good car in a more permanent sense, whereas Esse carro está bom might mean it is in good condition at the moment.

Is there any difference between bom and bem?