Worth is only used after verbs such as be, seem, look (as a predicative adjective). It means ‘having a particular value’, especially in money:
I wonder how much the house isworth?
About half a million, probably.
To be worth doing something is a common expression. It means that something is useful or important enough to do:
I haven’t had a reply to my email to Jane. Is it worth phoningher, do you think? (Would it be useful to phone her?)
You could try, I suppose.
We decided it wasn’t worth going all the way to London to buy books we could get on the Internet.
To be worth it means ‘to be of reasonable or good value for the price’:
A business class ticket cost £2,000, but it was worth it for such a long flight. It was very comfortable.
We use worthwhile before a noun (as an attributive adjective) or after verbs such as be, seem, look (as a predicative adjective). It means ‘useful’, ‘important’ or ‘good enough to be a suitable reward for the money or time spent or the effort made’:
Do you think working in a supermarket is a worthwhile career for a highly intelligent person?
We had thought of buying a bigger car, but we didn’t think it was worthwhile, since there’s just the two of us.