For 11 months, the UK will still follow all the EU's rules and regulations, it will remain in the single market and the customs union, and the free movement of people will continue.
The challenge for the government will be to get all its new rules and policies in place by the end of next year.
The UK still needs the EU's cooperation for Brexit. Agreement needs to be reached on many things, from trade duties, to thousands of regulations, to tax rules, not only for UK, but for Northern Ireland.
What happens if the EU doesn't cooperate?
If the EU won’t cooperate, there will be a no deal Brexit. There will be a clean break with the EU by December 2020.
A negotiated agreement is preferable but by no means assured.
Brexit is done on 31 January
Trade duties etc are purely trade discussions like NAFTA