Add contract labour?

How to add contract labor like carpenter, mason, plumber in my construction business?

Add an expense account named something like Contract labor in the chart of accounts. If you pay the subcontractors immediately, just use Spend Money in the Bank Accounts tab and allocate to that expense account. If they send you invoices that you pay at a later date, use Purchase Invoices to record them and enter another transaction when you pay to clear the Accounts payable. You will need to create the subcontractors as suppliers first.