If the file is of a type that your browser can read you will be able to see it right away. To open one you save it to your computer and then open it in the appropriate way. For example a text file would be opened in your wordprocessor. If you want to send picture files be sure to compress them so they don't take so long to send. Don't use a file type that your recipients may not be able to see.
Most scanners can save the files in different ways.
Select the file you wish to send. Then click on Attach. Send the email as usual.