Make sure you have followed the basic setup instructions on the Getting Started Page before proceeding to Step 2.
Go to File→Connect→External Data Feed to configure for an External Data Feed. If you are currently configured for a different feed, you must first disconnect from that feed in order to view External Data.
Once configured for the External Data Feed, go to Tools→Historical Data Manager. Use the default Format which is shown below. Set the Data Type to Last. Leaving the Time Zone of Imported Data set to UTC will enable the data to be imported based on your current time zone. Note that the data you are importing is tick data so it will be viewable on charts in either a Second or Tick based periodicity. If you want to view a minute based chart, check the box labeled Generate Minute bars from imported tick data. Here is an example of what the window would look like. The two bottom check boxes are optional:
Press the Start Import button and browse to the directory where you keep your text files and press Open.
Once you've imported your custom symbol data, NinjaTrader makes a few assumptions for you to set the Instrument up. Go to Tools→Instrument Manager to view those settings and make any adjustments you might need. Then select the Instrument from the list on the left and move it to the right using the arrow buttons. Then press "OK" to dismiss the Instrument Manager.
Go to File→New→Chart. In the upper left pane you will see your new Instrument. Select it and press New at the bottom of the window. Then set-up your chart Preferences and press OK. Remember that if you did not opt to Generate Minute bars from imported tick data, in Step Three above, you should choose a Tick or Second based periodicity.