(See the screenshot below).
Use the slider to reduce the duration.
(Optional) Click the "setting" button at the top-right corner.
(Optional) Here you can uncheck the "reduce FPS" checkbox. In that case frames per second will increase up to video FPS. The more FPS, the more weight of GIF. Uncheck all checkboxes if you want a high-quality GIF.
Click the pink button ("GIF") in order to convert a video to GIF.