The simplest way is to export data from FileMaker into some common format. To do this you need to open the file in FileMaker and for each table you need go to the layout associated with the table and use the menu to show all records and export.
Make sure to only export data fields (Text, Number, Date, Time, and Timestamp), because it's typical for FileMaker to have lots of calculated fields (Calculation and Summary). (To do this first go to File - Define Database, then to some table, sort files by type, and note the last data field.
This won't export container fields, but most apps don't store such data. It's still possible to export them too but it would require a custom script.
The next option is to use ODBC. It's 'next' because it's less convenient and usually slower.