The life cycle of an issue starts with its creation. An issue can be created via one of the following channels:
MantisBT Web Interface - This is where a user logs into MantisBT and reports a new issue.
SOAP API - Where an application automatically reports an issue into MantisBT using the SOAP API web services interfaces. For example, the nighlty build script can automatically report an issue if the build fails.
Email - This is not supported out of the box, but there are existing MantisBT patches that would listen to emails on pre-configured email addresses and adds them to the MantisBT database.
Others - There can be several other ways to report issues. For example, applications / scripts that directly injects issues into MantisBT database (not recommended, except for one-off migration scripts), or PHP scripts that use the core MantisBT API to create new issues.