As probably you have read before, you can decide which project fields you want to display per project in the Layouts. The layouts are like the project schemes in Jira.
Associate a layout to one or more projects
There are 2 ways to associate a project with a layout:
1. When you are creating or editing a layout:
2. From the layout manager:
In both cases, after click on "Associate projects" you just need to select all the projects you want to have that layout, and save.
You can see what projects are selected in "Selected projects" tab:
Switch layout in one project
You can change the project layout in the project tab. If you switch to another layout you don't lose the values of the fields.
After click in "Switch layout" you can choose from the different layouts created.