Instructional designers rarely create their own graphics. Instead, they use websites like the ones I discuss in this video to find what they need.
Then they use tools like Adobe Illustrator and Photoshop to modify the visuals as needed so that they work for their projects.
Here are links to some of my other videos that will help with graphics:
I highly recommend watching the Adobe Illustrator video if you're new to working with vector graphics.
Here are the links to the different graphics sites: