Family visas (IR and F) are designed for those who want to permanently settle in the USA based on their family relation with permanent resident or US citizen, who is sponsor of their visa. American citizen can sponsor spouses, children, parents and siblings, while permanent residents can sponsor only spouses and children.
The category of tour immigrant visa depends on your relationship as well as on the fact weather your sponsor is citizen or permanent resident. Some of these categories have limited number of visas per year.
In addition to these, there is also fiancée visa (K-1) which is a non-immigrant ie. temporary visa which allows you to travel to the USA and marry you fiancée who is permanent resident of the USA.
The basic conditions that need to be met for a work visa are:
Family visa is designed for bringing families together: if one family member is a citizen or permanent resident of the USA through this visa other family members can come to USA so they can live together and study or work. Family visa allows permanent residency ie. you can become permanent resident with this visa and if you meet certain condition later you could become US citizen. If your petition for immigrant visa is approved through close relative (sibling who is a US citizen), your family members (partner and children under 21 years old) also have opportunity to apply for family visa and accompany you.
Family visa is a permanent visa, while fiancée visa is temporary. Fiancée visa allows you to get married with an American citizen within 90 days from the day of your entry into the USA.
Application for family visa goes online through website of US Citizenship and Immigration Services – USCIS. American embassy in your country does further processing which includes interview in consular section.
Fee for a petition for immigrant visa is 535USD, visa fee for family visa application is 325USD while visa fee for fiancée visa is 265USD. Processing time depends on each case especially if you are applying for a category with limited number of visas per year.