Nela,
1) You need to pass following Journal Entry In Transaction-->Financial-->General.
Expenses A/c Dr $$$
To Expense Clearing A/c (PO Clearing A/c) $$$.
This way you will Accured your expenses.
2) When you are ready to make Invoice for FedEx make sure you will change A/c in Distributions screen
Expense Clearing A/c Dr $$$
To Accounts Payable $$$
3) On Payment you don't have to make any changes but it entry will be
Accounts Payable A/c Dr $$$
To Cash/Bank A/c $$$$