Once you allow Teamwork Chat to access 3rd party file storage apps (for example Dropbox, Google Drive, OneDrive, Box.com) you'll have the ability to attach & send files through Teamwork Chat from those apps.
To set up the access, you can create a new conversation or go to an existing one, and tap the attachment icon to the left of the message field:
By default, you'll see the options to take a new photo/video using your mobile device or attach an existing image/video from your gallery.
By clicking “More”, you have the option to attach items from 3rd party apps already installed on your device.
Once you enable other apps in the 'Locations' manager, you'll have the option to choose items from each (including, but not limited to the following):