To build our game into WebGL, go again in Build Settings, WebGL and click on Switch Platform.
As we can see, Unity have to recompile the project:
This also can take a little times.
After this process, now we are raedy to Build in WebGL.
We have yet a little problem here
Enter in the Player Settings
Now we are in WebGL section.
The resolution by default is 960 x 600, for display it in a Web Browser.
Before make anything, we have to change the Color from Linear to Gamma
After Unity recompile, close this window, and in then Build Setting just click Build.
Choose again a right folder where build the project, select it and let the Unity build the project.
If we go inside the folder, we have 3 files to drag in the site to upload the project in the Web Browser