How can I make custom graphics on my PC?
If you are looking for paint software, there are Paint.net, Gimp, Photoshop, and dozens of others. For animations, there are animation studio software you can use like Anime Studio Debut, As others have mentioned, being more specific would give you better results as it all depends on what exactly you are looking to do.
For alternatives for Adobe Illustrator, you can try these, these, these, or these alternatives. I do not have experience with any of the Illustrator alternatives, but also what one person lies may not be the same for others.
Kindly be a bit more specific with your question rather than being generic to enable us to give a proper response to your query.
what do you mean by make custom graphics?