διαβάζω, σπουδάζω, μελετάω, μαθαίνω

Hello!
διαβάζω, σπουδάζω, μελετάω, μαθαίνω...
Which verb to pick usually causes troubles to beginners.
Let's "unravel this word mystery" here once and for all!
Feel free to add any comments or questions below 😀