Q:

How does "suku" (empty) become "suite"?

Just started learning Japanese two weeks ago. I have so many questions. If my question sounds a little silly, please bear with me. 
I just learned that adjectives + desu and verb + imasu. But how do I know if a word is verb or adj. without checking dictionary every time. 
For example: kibun ga warui desu (is sick); onaka ga suite imasu (is hungry)
Here, the locations of "warui"and "suite" in the phrase look the same to me. Literal translation is "the feeling is bad" and "the stomach is empty". When I try to memorize which phrase ending up with "desu", and which ending up with "imasu", I got very confused.
Someone told me the original form of "suite" is "suku". Is there any rules of verb transforming to adj.?
Thanks!

A:

After understanding the basic grammar, you can usually tell if an unfamiliar word is a verb or an adjective just by looking at how it's used in the sentence, including its conjugation pattern. You already know masu only attaches to a verb! (Of course you can do the same thing in English, too. By looking at "You have narvolooned", you can tell narvoloon is used as a verb even though such a word actually does not exist.)
Please not that the very literal translation of "Onaka ga suite imasu" is "(My) stomach has emptied" rather than "stomach is empty" or "I am hungry". There is no (transformed) adjective in this Japanese sentence. That is, in English, an adjective is normally used to express this idea, but in Japanese, a verb is used instead. (The opposite is also possible. You may already know you have to use a na-adjective to say "I like cats" in Japanese.) Imasu is a subsidiary verb that only attaches to the te-form of a verb, and suite is the te-form of the intransitive verb suku meaning "to become empty" or "to be less crowded".

