You can choose the way you are going to work with your documents under Drive Settings > Settings for Working with Documents:
This option allows to open & edit documents online via Google Docs, MS Office Online or Office 365.
Locally option allows to open & edit files via programs installed on your local computer. Each time you will click on any file in Bitrix24 - the file will be automatically opened inside applications installed on your computer (e.g. file will be opened in Excel program installed on your computer). Please note – files opened this way won’t be saved to your Bitrix24 by default. We recommend to enable Bitrix24 Drive synchronization, so that the files that you edit locally will be automatically synchronized to Bitrix24.