There is a very extensive compilation of all the functions available in the macro language on the ImageJ website (http://rsbweb.nih.gov/ij/developer/macro/functions.html). In this section, we are offering a brief explanation of some of the operations that you are most likely to use. Instead of just listing the name of the necessary functions, we will ask some common questions and then answer them using code.
Note that finding out what command does a specific function is very easy: just start the recorder and run the command you are interested on running in your macro. You can then copy and paste the resulting line and modify the parameters accordingly.