Double-click the J icon to start J. Your J session should look something like this:
The window labeled 1.ijx is an execution window. You type J sentences into the ijx window and J executes them when you press enter and displays the result.
Type the following line into the ijx window and press Enter.
2 + 3
The sentence is executed and the result is displayed. Type the following line and press Enter.
5 - 3
Your session should look something like this:
Lines that you enter are indented three spaces and the J answers start at the margin.