Zukertort Opening is a chess opening with the ECO code A04. It goes 1. Nf3. White opens with 1. Nf3 (the Zukertort/Réti knight move). After 1 move it is Black to move. The lesson on the board explains every move of the line and lets you play it yourself; it is free.
In chessGM's opening book this position continues with 1... d5, 1... c5, 1... Nf6.
White starts with 1.Nf3, a flexible move that develops and controls e5 and d4. White can later go into many different openings.
chessGM has a full course for this line: open the Zukertort Opening course lesson.