The ringtone editor is accessed by clicking the tones button on the right of the toolbar or by selecting it from the view menu.
The RTX file format is compatible with Nokring tones (.txt) and which are available on the web. The specification for RTX files is here.
Example:
Alert:B715:32C,32P,32D,32P,32E,32P,32F,32P,32G,32P
This file describes a ringtone whose name is 'Alert'. The control section sets the beats per second at 715, and the note definitions describe a series of 5 notes and 5 pauses of length 1/32 of a full note. Each note is constructed of three parts: the note fraction (optional), the note name itself or rest, the octave to use (optional). If optional entries are omitted then the default is used from the section at the start of the ringtone.
Most phones have a 'preview' mode when receiving tones via a cable, however some phones do not support this. For this reason, there is an option to insert the ringtone direct into the tone memory in the phone. When you select this option, you will be asked the position to enter it into - this should usually be set to 1.