Transactions protect important flows like payments, inventory, and account updates. If one step fails, the database rolls back the whole group instead of leaving half-written data.
ELI5
Think of Transaction as a labeled box where an app keeps important things. A group of database changes that must succeed or fail together.
In practice
Use it when a feature reads, writes, migrates, validates, or audits stored information. In practice, define the owner, input, output, and failure mode before you rely on it.