We have to add the scenes that we're going to use to the build settings before we can test our code works, so click on File | Build Settings, and then click on Add Current. You'll see the scene name appear in the Scenes In Build area, now drag the TitleScreen and the GameScreen scenes into the same window and their names will appear there too. Close the build settings window and click on the play icon in the top-middle of the Unity screen. If all has worked as expected you should be staring back at a plain blue screen. That's actually a good result as it means your SetUp scene is working as expected and has loaded the TitleScreen scene immediately, and the blue screen you see is from the background color of Main Camera in that scene.
Argentina
Australia
Austria
Belgium
Brazil
Bulgaria
Canada
Chile
Colombia
Cyprus
Czechia
Denmark
Ecuador
Egypt
Estonia
Finland
France
Germany
Great Britain
Greece
Hungary
India
Indonesia
Ireland
Italy
Japan
Latvia
Lithuania
Luxembourg
Malaysia
Malta
Mexico
Netherlands
New Zealand
Norway
Philippines
Poland
Portugal
Romania
Russia
Singapore
Slovakia
Slovenia
South Africa
South Korea
Spain
Sweden
Switzerland
Taiwan
Thailand
Turkey
Ukraine
United States