Summarize this article:

Type it in the "To" field.     Most of the pictures on your computer will likely be stored here. Most Internet service providers (ISPs) restrict the size of attachments, so if you're sending multiple pictures, it may be a good idea to send several emails with a few attachments.  Your pictures will be sent to the person to whom the email is addressed.

Summary:
Open the Mail app in Windows 10. Click ⊕ New mail in the upper-left corner. Enter the recipient's email address. Add a subject in the "Subject" field. Type the body of the email message. Click the Insert tab at the top of the screen. Click Pictures. Click the Pictures folder. Choose the picture(s) you want to send. Click Attach. Click Send in the upper-right.