For readers who would like a basic, very easy-to-use online diagram application, draw.io could be the answer. The service utilizes simple drag-and-drop techniques to arrange images for non-professional users. First select a system to which you will save your diagrams (possibilities include Google Drive, OneDrive, Dropbox, your computer, and your browser). Then select Create new diagram. From there, select images from the dozen or so categories on the left hand side of the screen and drag them to the workspace, where you can change their color, increase or decrease line widths, and generally edit the style to suit your needs. There is also a helpful Quick start video that readers can watch to help them understand the program. The application is free and does not require a sign up or any other commitment.