CREATE TABLE users(
id int, 
username varchar(30),
password varchar(60),
PRIMARY KEY(id)
)

CREATE TABLE ➔ Create a freaking table! PRIMARY KEY(x) specifies which column is the primary key.

CREATE TABLE users(
id int NOT NULL AUTO_INCREMENT, 
username varchar(30) NOT NULL,
PRIMARY KEY(id)
)

NOT NULL ➔ Specifies that your table column cannot be empty (aka NULL).
AUTO_INCREMENT ➔ Automatically increases by 1 every time a new row is made.