The initial Session dialog, displayed at each start of Ardour, consists of several consecutive pages:

Open Session Page

The Session Setup Dialog
The Session Setup Dialog

On this page, an existing session can be opened. Any snapshot of a particular session can also be accessed by clicking on the arrow next to the session name to display all snapshots, and then selecting one.

If the session is not displayed in the Recent Sessions list, the Other Sessions button will bring up a file selection dialog to navigate the file system.

Alternatively, a New Session can be created.

New Session page

The New Session Dialog
The New Session Dialog

This page allows to type in the name of a session, select a folder to save it in, and optionally use an existing template.

Under Advanced Options, some fine tuning can be done, like selecting whether Ardour should create a Master Bus, or a Control Bus, and how many channels the output should have.

Other options also decide whether Ardour should automatically connect all inputs to the hardware's physical ports. Ardour will do so sequentially and in round-robin fashion, connecting the first track's input to the first input of the hardware and so on. When Ardour has used all available hardware inputs, it will begin again with the first physical input.

The number of hardware channels used by Ardour can also be limited.

By default Ardour will connect all tracks and busses to the Master Bus if there is one. However, it can also be told to automatically connect each output to the physical outputs of the interface or sound card, and limit the number of physical outputs used, as above.

Audio/MIDI Setup

The Audio/MIDI Setup Dialog
The Audio/MIDI Setup Dialog

This window exposes the different audio options to be used by Ardour for the current work session, for hardware and software and is made of:

Audio System Depending on the operating system, Ardour can possibly use different audio systems, e.g. on Linux, both ALSA and JACK are available.
Driver On Mac OS X this will typically be CoreAudio. On Linux usually this will be either FFADO or ALSA, depending on whether or not a firewire device is used. Advanced users on all platforms may also use NetJack which provides network audio I/O.
Device The selector should show all availiable interfaces provided by the driver above and which are capable of duplex operation.

When using an Intel Mac running OS X and the builtin audio interface, its separate input and output devices must be merged first into a single "aggregate device" before Ardour will be able to use it.

Sample Rate The selector will allow to select from any sample rate supported by the device selected above it.
Buffer Size The size of the buffer used by the audio interface can be adjusted to allow for either lower latency, or lower CPU usage and higher latency.
Input/Output Channels Specifies the number of hardware channels to use. The default is all available channels.
Hardware Input/Output Latency Specify the hardware delay in samples for precise latency compensation.
Calibrate This button runs a semi-automated guided process to obtain precise hardware latency measurements for the above option.
MIDI System Selects the MIDI driver to use. On Mac OS X, this will be CoreMIDI. On Linux, it can be changed between two legacy ALSA drivers or the (preferred) new JACK+ALSA implementation.