when we check any area of audit i.e any income expense asset liability first we check procedures set by entity for such income expense asset liability which ensure smooth functioning with accurate accounting this is called test of controls or compliance procedures
for example when we check bank reconciliation we are checking a internal control system which ensures all receipts and payments are recorded so it is test of controls.
but when I select receipts or payment and trace it to vouchers and registers to ensure there authenticity and accuracy, that means we are focusing on individual income expense asset liability not there procedure then it is substantive procedures
test of control only gives us overview whether accounting will be proper or not test of details will confirm / substantiate whether actual things are proper or not.