After creating an algorithm you will probably want to run the algorithm. Basically there's not much to say about running algorithms. To run an algorithm just choose Run Algorithm from the project menu (note that an algorithm editor must be active, otherwise the menu item Run Algorithm will be greyed out).
Your algorithm may print some messages about its state or results. These messages are shown in the console which opens automatically.
Note: normally the console is brought to front automatically if you select Run Algorithm from the menu. But sometimes this will not happen for some unknown reason. In this case you will have to activate the Console manually. Otherwise you won't see any output of your algorithm.
Running an algorithm is actually running a Java program. To view and edit the program parameters choose Run in the drop down menu in the Java perspective.
In the window that appears you can change the Java program parameters for your algorithm.