"How are you today?"
Duo gradually present new things, so you WILL make mistakes and you WILL have unanswered questions at some points. That is the teaching method. Very natural as if you were in an environment in which you dont know the language, you look for hints and paterns (maybe a little help) and that is how you learn! I personally really like it because it doesnt overwarm me with lots of info, it just comes naturally after practicing consistantly during some time.
怎么样 is used to ask "how something is". Literally 怎么 = how/why and 样 = kind, type, way, manner. So I think "How about it/this" is a pretty good way to think of it. It can also be used to ask someone's opinion about something by putting it after a statement: 去喝咖啡怎么样？"How about going for coffee?" or literally "go drink coffee, how about it?"
An adjective can't stand alone as the predicate of a sentence. That's the basic rule. So if there are other words in the predicate, you don't need 很 unless you actually want to say "very". If the adjective would otherwise be alone as the predicate, the common way to fix this problem is to add 很 as a grammatical filler word.