How can I learn C from scratch?

Answer 1

You can start here.
https://www.sololearn.com/learn/1139/?ref=app

Answer 2

For C, as I started, I would suggest you a few sources as follows:
1. Programming in ANSI C by E. Balagurusamy
2. Let us C by Yashwant Kanetkar
3. Sololearn
4. Passion for Programming
5. Determination to learn

*If you can't buy these books, you can find PDFs of these books available on Google.

That's all you need along with a PC, of course!
Good luck!
Happy coding! ))