What each field means
Every zone has exactly one SOA at the apex. MNAME is the primary master nameserver. RNAME is an admin email with the first dot standing in for @. Serial must increase when you publish a change so secondaries know to transfer. Many operators use YYYYMMDDNN. Refresh, retry, and expire tell slaves how often to check and when to stop serving a zone they can no longer reach. Minimum TTL (negative caching TTL in modern usage) controls how long NXDOMAIN can be cached.
If two DNS hosts disagree about the serial, you are looking at a split-brain zone — usually leftover delegation. Check NS records next.