Sometimes employees go outside for company's work and company pays some amount for their expenses in advance. In that time, the employee can create Employee Advance form and the expense approver can submit the advance record after verification. After Employee Advance gets submitted, the accountant releases the payment and makes the payment entry.
After saving Employee Advance, Employee should [Assign document to Approver](/docs/user/manual/en/using-erpnext/assignment.html). On assignment, approving user will also receive email notification. To automate email notification, you can also setup [Email Alert](/docs/user/manual/en/setting-up/email/email-alerts.html).