First of all, you have to open your Apple Mail. You can simply open it by clicking ‘File’ menu and then selecting ‘New Message’.
When the Apple Mail will be opened, just enter the recipient’s email address, the subject of the email and your message. Then, you will have to select your email account from the drop-down list which appears when you will click ‘From’.
After filling the necessary information, you have to click on the square paper clip icon which is displayed at the top right corner of your email screen. Then, find the file which you intend to attach to your email and click ‘Choose File’ option. If you have multiple files to attach, you can do it by repeating the process.
Now, you have to click on the square airplane icon which you can find at the top left corner of your email screen in order to send your message along with the file or files which you have attached to it.