DataTable() or dataTable()?

Sorry if this question seems strange, i'm a bit noob on javascript xD

What is the difference between $( selector ).DataTable() and $( selector ).dataTable();? and what is the correct way to use the plugin

I ask this because i couldnt make ajax to work, later i realized that the example is $( selector ).DataTable(); and i was using $( selector ).dataTable(); but i cannot understand the need to use 2 function names with only a capitalization diference

Is it for compatibility between datatable versions?

Regards...