Zukertort Opening is a chess opening with the ECO code A05. It goes 1. Nf3 Nf6. White opens with 1. Nf3 (the Zukertort/Réti knight move) and Black answers 1... Nf6. After 2 moves it is White 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 2. g3.
White starts with 1.Nf3, a flexible move that develops and controls e5 and d4. White can later go into many different openings.