After opening fusion, click on sketch icon in the upper bar as in the following picture, then select which plan you want to draw on
Use the icons in the ribbon to select which shape you want to draw then draw it. And use the modification tools to modify your sketch as you need. And constrains tools to add the required constrain.
Make sure to follow the following rules
By using extrude icon you could convert any 2D sketch into 3D model
You could add appearance to any 3D model by many ways:
After adding the appearance, you can press on the icon of render or in canvus render to start rendering the image.
pay attention: if you render in canvus Do NOT move any thing in the screen or even change the view, as if you did, the render would start again from the begining.
To see all the steps from starting sketch to rendering the image Watch this video