Programming means writing code. A book is made up of chapters, paragraphs, sentences, phrases, words, and finally punctuation and letters, likewise a program can be broken down into smaller and smaller components. For now, the most important is a statement. A statement is analogous to a sentence in a book. On its own, it has structure and purpose, but without the context of the other statements around it, it isn't that meaningful.
A statement is more casually (and commonly) known as a line of code. That's because statements tend to be written on individual lines. As such, programs are read from top to bottom, left to right. You might be wondering what code (also called source code) is. That happens to be a broad term which can refer to the whole of the program or the smallest part. Therefore, a line of code is simply a line of your program.
Here is a simple example:
let hello = "Hello"; let world = "World"; // Message equals "Hello World" let message = hello + " " + world;
This code can be executed by another program called an interpreter that will read the code, and execute all the statements in the right order.