The functionality is available within the context of the feature you're using. If it's a Word document you open the document, click the share icon and click "Send Attachment". Apple's Pages also has a Share icon that even lets you easily convert to Word, PDF, or ePub format before sending.
For attaching whilst composing an email in Gmail (what I use) there's an "Attach" icon that lets you attach photos or files from Google Drive. Whilst Apple's Mail lets you click the cursor on where you want to add the Photo/Video.
For attaching whilst composing an email in Gmail (what I use) there's an "Attach" icon that lets you attach photos or files from Google Drive. Whilst Apple's Mail lets you click the cursor on where you want to add the Photo/Video.