ASCII data is widely available, and is many ways the original data format. Many free sources of ASCII data are available, and many data providers provide an export facility from their propietary format into ASCII format, and so ASCII data is often the data format of choice for users getting started with Sentient Trader (although Ninja Trader has recently changed that) .
Take a look at the second part of this tutorial for information about sourcing ASCII data.
Take a look at these videos for more information about working with ASCII data in Sentient Trader:
An introduction to ASCII data:
Creating charts with ASCII data: