To capture the movement of clouds across an open sky usually requires a long exposure time of several seconds. This means you'll need a tripod and, if you're shooting in the daytime, probably a neutral density filter over the lens to cut the light level down to enable slow speeds. Jesse Estes took this beautiful lake view in Oregon, USA, at sunrise. With a B&W ND3 Grad filter fitted to his lens, plus a -3 stop ND grad filter (to further darken the sky) he needed an exposure of 251 seconds. The cloud movements during this time have recorded as blurred streaks.
Nikon D300, Sigma 10-20mm, 251sec @ f/8, ISO 200, B&W ND3 Grad, -3 stop ND grad Jesse Estes