To give a warning or reminder firmly; to make sure someone understands. Can also mean literally to drive in a nail.
上司は納期を守るように部下に釘を刺した。
The boss warned his subordinate to meet the deadline.
念のため、取引の条件をもう一度確認して釘を刺しておいた。
Just to be safe, I double-checked the terms of the deal and made sure to emphasize them.
古い戸を修理するために、大工が板に釘を刺した。
To repair the old door, the carpenter drove nails into the plank.