You can draw in a chat, which is the quickest way to show working or a shape you cannot easily type.
Drawing
Click the + button below the chat box and choose the drawing option. Sketch with a mouse, a finger or a stylus, then add it to your message.
Say what you want help with as well as sending the drawing. "Here is my working, where did I go wrong?" gets a better answer than the picture on its own.
To send a photo of work you did on paper instead, use + and pick the file, or use Upload from phone to scan a QR code and take the photo on your phone.