One year of compulsory service, worked wherever the state posts you, by every Ghanaian who graduates from an accredited tertiary institution and is under 40 when the service year begins.
It is governed by the National Service Authority Act 2024 (Act 1119), which repealed the 1980 Act and turned the old National Service Scheme into the National Service Authority. Almost nobody says “NSA” - the year is still “national service” and the people doing it are still “NSS personnel”.
The allowance is ₵715.57 a month, set by the Ministry of Finance rather than negotiated, and it is the single largest complaint about the institution.
You need the certificate at the end. A great many Ghanaian employers ask for it, and some will not process an application without it.