There are three options for attachments in Gmail. Firstly, you have the paperclip icon as is common across the web. Select this to attach a file from your computer.
Secondly, you can select the Google Drive icon to attach a file straight from your Google Drive and thirdly select the Image icon to search through your Google Photos account and attach a photo.
How do I save an attachment?
When looking at the attachments on an email, there are two icons on the right-hand side. A download arrow and the Google Drive icon. Select the Download button to download all attachments, select the Google Drive icon to save the attachments straight to your Drive.
If you hover your mouse over a single attachment, the two icons will appear. Select the Download icon to download just that single file and select the Drive icon to save that file straight to your Drive.
Is there a size limit for attachments?
Yes, this is 25MB. You will not be able to send an email if the attachment/s exceed this size.