Can I create a correlation between inventory and customer database?

Yes, this is extremely simple to do in FileMaker, as long as you have fields in each table that you wish to link, that contain matchable data (ie primary keys, unique ID, customer number or similar)

Of course, you can create a relation between data and use it in other context. For a better answer, need more info, also in portuguese if you prefer!

A fully qualified field name in FileMaker includes the table occurrence and the field name, separated by a double colon, so the answer is a definitive "yes". Your question, however, alludes to needing the same data in 2 different databases. If that speculation has merit, the you can connect through external file references, the 2 databases and refer to that required field directly, avoiding duplication of data.

Yes, that is relatively easy with Filemaker Pro