Drag a copy of the Excel spreadsheet onto the FileMaker 15 application icon.
FileMaker will then produce a file with all of the data from your Excel spreadsheet. This imports the data and sets up a table. It does not replicate calculations that you may have defined in various cells nor does it try to replicate how you may have set up column widths and formatting, but it's a starting point to work from in building your database.
Keep in mind that FileMaker is not a spreadsheet program. The harder you try to replicate exactly the same set up in FileMaker as you have in your Excel spreadsheet, the more likely you are to be frustrated with the results.
The first step is easy. Just open the spreadsheet will FM. You will be presented with an option to treat the first row as field names, which is usually the best choice. Try that and go from there. You do not destroy your spreadsheet in the process, so if you need to you can always start again.