Basic Mixing : Sends : Send Path Selector Choices
 
Send Path Selector Choices
The choices available in track Send selectors include bus and output paths.
Internal Mix Busses
Pro Tools | First provides 24 internal mix busses for routing signals internally. Internal bus paths are useful for submixing and processing with plug-ins.
Hardware Outputs
Hardware sends are often used for headphone cue mixes, or for sending signals to external effects processors.