Hello,
My employee requested for advance.
I approved and gave money to him, accounting entry: debit advance to employee/credit cash on hand
My employee used that amount of money to buy things with invoices, accounting entry: debit expenses/credit advance to employee.
He gave me the rest/I payed him more.
Can anyone please tell me how to do these steps in Odoo?
You can do it by manually posting the corresponding accounting entries or by using the payroll and expense features. Please make yourself familiar with the documentation first.