For your spouse/unmarried partner to enter the UK and stay for more than six months you will require a Settlement Visa. A Standard Visitor Visa is fine if you want to stay for less than six months.
For your spouse or partner to apply for Settled Person Visa they must be married or living together for more than 2 years, to a person living permanently in the UK who is either a British Citizen, has settled in the UK, or who has asylum or humanitarian protection in the UK.
It usually takes about 12 weeks to get a decision and they have to pay the health surcharge (which entitles them to medical treatment from the National Health Service).
With a Settlement Visa they can work in the UK but not be able to access public funds. They may be able to extend their visa and settle in the UK permanently (Indefinite Leave to Remain).