Short answer: 20 m/s at 45° from level ground travels 40.79 m, peaks at 10.20 m after 1.44 s, and lands 2.88 s after launch. Both distance and height are the same because sin 45° and cos 45° are equal.
The two components
Splitting the launch into v_x = v cos θ and v_y = v sin θ is the whole method: horizontal motion is constant speed, vertical motion is constant acceleration, and the two are joined only by the clock. The page prints both components so the split is visible rather than assumed.
Worked example
A football kicked at 25 m/s and 35°: v_y = 14.34 m/s, flight 2 × 14.34 ÷ 9.80665 = 2.925 s, range 20.48 × 2.925 = 59.9 m and apex 10.49 m. Air resistance would cut that by roughly a fifth in a real match, which is why the assumption is printed under the result.