Once you have submitted your expenses, the lines can be approved, queried, put on hold or rejected.
Queried and rejected are the only two actions that then require further input from you. You should receive an email advising you of their status (though this depends on system setup).
Rejected expenses will appear in your expenses view with the number of lines noted in the rejected column:
Notes are required by the approver in order for them to reject your expenses. So, if you open up the sheet lines, you will see notes.
However, the only action available for you is to delete the expense line.