The third step to settling in the UK under the Spouse visa category is the application for indefinite leave to remain in the UK. Indefinite leave to remain also means permanent residency in the UK.
You have to make an ILR application 28 days before the expiry of your leave to remain (granted at the extension stage). Technically, you may make this application after 5 years of living in the UK as the spouse/partner of your sponsor.
Indefinite leave to remain in the UK means that you are not subject to immigration control any longer. You would be allowed to work and live in the UK for as long as you may choose.
You would retain your nationality and still hold the passport of your country of nationality.