The subclass 176 visa is a different class of sponsored migration. Instead of a 457 work permit sponsored by an employer or an Employer Nominated Permanent Visa this is more like the the 175 visa - a skilled visa that isn't tied to anyone. Except this visa is tied to a sponsor. With the 176 visa your application is "sponsored" by a relative living in Australia who meets the necessary criteria OR a Government Agency of an Australian State or Territory.
Its unusual to have these two categories together, but the general thought is that if you meet the Skilled Occupation List (the very same used for the ENS and the 175), but don't have the necessary points to get a 175, then you can still come in if either
(a) the demand is great enough (i.e a Government Agency sponsors you) or
(b) you have a good support network (i.e. a relative sponsors you). This will need to be an eligible relative currently living in Australia who is related to you, your spouse or your interdependent partner.
The points required for a 176 permit are lower than that for the subclass 175 Skilled Independent visa. You can check your point score on the Department of Immigration Subclass 176 Sponsored Migrant Visa Calculator.
As soon as you have this visa, you and and dependants included on your application can live as permanent residents of Australia. for a period of 5 years. You can eventually apply for citizenship. If you want to leave Australia and return provided you've spent enough time in Australia during that 5 years you can get a Subclass 155 Residents Return Visa.