I don't know how to use 'worth correctly. Can you take a look at the following sentences?
1. Doing voluntary work is worthwhile OR worth.
2. It is worth to do voluntary work OR doing voluntary work.
3. Even though we have to sacrifice a bit, I think it worth it.
"Worth" is used as an adjective and a noun also.
As an adjective, worth is followed with noun/ V-ing.
The 3 examples you took could be correct in this way:
1.Doing voluntary work is worthwhile.
2. It's worth doing voluntary work.
3. Even though we have to sacrifice a bit, I think it's worth it.