To submit your expenses you need to add your expenses to a report. You can find more information about how to add the expenses to a report on this support page.
I work with the app:
In the app you will find the submit button on the following places (left image for Android, right image for Iphone):
If you press the submit button you will see the person who will approve your report,. You need to press the submit button one more time to confirm:
I work with a browser:
To submit a report you simply need to press one button:
If you click on submit you will see the person who will approve your report.