At times it can be helpful to work from a reference image. To add one in Fusion 360 click the "Insert" icon in the toolbar. In the menu that appears, click the button that says "Insert from my computer..." and then the plane on which you would like to view your reference image. Once you have positioned your image, press OK.
A new dropdown menu will add a new section called "Canvases." You can toggle the visibility of your reference image as well as delete it in this menu.
If you know the exact size of an object in your image you can calibrate the canvas to match. To set the image size right click on the image under Canvases in the browser and select Calibrate.
After you click Calibrate you will be asked to select two points on your image. A box with the current distance between those points will appear. Type in what the actual value should be (in millimeters) based on the physical object and the whole canvas will scale to match.
One great feature of Fusion 360 is the timeline. The timeline tracks the changes and commands that are made throughout the project and can be used to revert to a previous version of the model or edit a feature that was previously applied.