the app does not appear

I have access to the dashboard, but when I publish it, the app is all white.
Can someone help me!!

Most likely you have all of the Tabs marked as invisible. In the builder app view, float your mouse over the Tabs in the left-hand panel. Take a look to the right of the Tab name, you will see an eye icon. If it has a line through it, it indicates it is not visible in the app.