To qualify as a dependant, you must be the spouse/partner or minor child under 18 of the main work visa holder. Other relatives usually don't qualify. Dependents are typically granted leave to remain in the UK for the same period as the main visa holder. After 5 years on a dependant visa in the UK, dependants can apply for Indefinite Leave to Remain (ILR). In some cases, they can apply for ILR simultaneously as the main visa holder. Dependents are prohibited from working or accessing public funds unless the main visa holder's work visa allows dependants to work (like the Tier 2 visa). Dependents must prove they can support themselves financially without working or accessing public funds. The main visa holder must provide accommodation and maintenance in the UK—additional English language and Life in the UK test requirements for ILR applications by dependants. So in summary a visa provides a route for family members of work visa holders to live in the UK, but does impose restrictions around working and accessing public funds. The option to eventually apply for ILR is there after meeting the requirements.