If you are using the webform module you can download submission's results in csv/xls files. if you want to do that go to:
content => select the webform you need to export => click on the result tab => finaly click on the download button.
If you need more flexibility like exporting multiple webforms Which fulfill certain conditions.
Take a look at the Forena Reports module and this postpost in which a detailed exemple is given by a co-maintainer of the forena module.