Welcome to the forum derelttil.

For clouds, create a ball, then give it a 'volumetric' MAT. Copy the ball and place it slightly lower the the original; and make it slightly smaller. Repeat the same process till you have a string of balls all slightly getting smaller, and then render. You might need to adjust the MAT a little, and bear in mind that it will take a long time to render.

Another way is to us a 2D plane and apply a smoke from a chimney picture to it, and placing that in your scene. This will look more realistic maybe , and render so much faster.