Enter all cash and checks you have received since the ending date of your last report.
Do not report invoices you have sent out, but have not yet been paid for unless you are on an accrual accounting system.
Most installers are on a cash basis system, which means that income is not income until you have actually been paid and an expense is not an expense until you have actually paid for it.
An accrual system is where income is income when it is incurred and the same with expenses.
It does not matter when you are paid or when you pay an expense. If you are not sure which you are on, take out your last tax return and look at schedule C. On line F you will see boxes for Accounting Method. See which box has been checked.
Once you use a particular accounting method, you must stay with it unless you get permission from the IRS to change.