This assumes you have already created a migration plan.
In the OpenShift Cluster Application Migration Tool, expand Plans, select the plan you want to stage (plan001 in this example), select the three dots and select Stage.
While the plan is being staged, the status should be "Stage Running".
If the plan is successfully staged, the status should become "Stage Succeeded".
You are now ready to migrate the migration plan.
If the staging hangs indefinitely, select the three dots and then select Cancel. While the staging is being cancelled, the status should be "Canceling Stage" and "CancelingEnsureMigratedDeleted".