Assets:

1. Cash: currency, coins, checking accounts, and cheques that were from customers. 
2. Prepaid Insurance: It's pretty much a contract that has been paid for in an advance. It shows the amount that has paid but doesn't expire due to the balance sheet date
3. Petty Cash: Cash that are given for supplies.. 
4. Supplies: Cost of supplies at one point in time
5. Accounts receivable: A combined amount of debit balance

A doubtful account is the credit balance in the contra asset account.
The difference between assets, liability and equity is that assets control or represent the different receiving of cash, liability is a formal payment and equity is earnings.