Pipelines get scheduled automatically by default. Please see the knowledge base article in the Also see section below. Here we'll see how to disable automatic scheduling.
Unchecking the "Automatic Pipeline Scheduling" checkbox above disables auto scheduling. Actually this is the same as marking first stage as manual. We have just surfaced the option at a pipeline level to make it easier to spot. Please note though that this isn't really a pipeline level configuration. For example, if this is pipeline is based off a template, the checkbox above will be grayed out to indicate that it can only be toggled by editing the first stage in the template.