Queue

Open a photo for editing, tweak it, click on Save current image, add it to the tail of the processing queue and click OK. Go to the Queue tab. You will see your photo there, waiting to be processed.

The File format panel resides in the top-right side of the Queue tab. You can save to JPG (8 bits per channel), TIFF (8 or 16 bits per channel) and to PNG (also 8 or 16 bits per channel). You can also select Save processing parameters with image - this options writes a sidecar file with all your adjustments made to that photo in a plain text file. This file will have the same filename as your photo, but it will have a ".pp3" extension.

You can set where you want the resulting JPG, PNG or TIFF image saved to by entering an appropriate template in the Use template field in the Output Directory panel. To find out how to create a template, hover your mouse over the Use template input box and a tooltip with an explanation will pop up:

Alternatively, you can save directly to a specific directory, but in the long run it is much easier to use a template.

On the left you see a Start/Stop processing button, and an Auto start checkbox. If Auto start is enabled, every time a raw is sent to the queue, processing will start immediately. Usually you will not want this, as this will use up your CPU on developing the photos in the queue, and as a result all adjustments you do while the queue is running will take much longer to get applied so that you can see their effect in the preview - RT will become sluggish. If Auto start is unchecked, you will have to activate the queue manually by clicking the Start processing button once ready to do so. You can pause the queue by pressing the Stop processing button, but RawTherapee will first finish processing the current photo.

You can delete the contents of the processing queue by right-clicking on a thumbnail and choosing "Select all > Cancel job".

You can exit the program and restart it later; the batch queue will still be there. The queue can even survive a crash of RawTherapee, as the batch queue info is written to disk each time you add a photo to it, each time a photo is done processing and each time you delete a photo from it.