I met many lcd commonds, how and when to use that?
This one is not like the others.
None of these commands/functions are "standard" Arduino functions. In a sketch where you see them used, they will be provided by a library. There are many different libraries for the many different models of LCD that can be used with Arduino. Often there can be more than one library for the same model of LCD. How these functions are used depends on which library they belong to. If you share with the forum the line in the sketch that #includes the library, even then, it is not always possible to say which library is being used and how the functions of that library should be used.
To be clear with your question to the forum, you must give the web address where the library can be downloaded, or if using the IDE library manager, the name of the library author.
If you find code on the web, sometimes the author of that code does not make it clear exactly which library they have used. To deduce which library that was can sometimes require the skills of Sherlock Holmes!