What RTL means
You have spent two modules drawing circuits and reading truth tables. Real chips are not drawn by hand. They are described in text with a hardware description language, and a tool turns that text into gates.
The style you will write is called RTL, register transfer level. It describes what a circuit does, and synthesis works out the gates that do it. Everything you already understand, MUXes, adders, decoders, you are about to write down.
A description is not a program. It does not run top to bottom. It lays out hardware that is all active at once.