Amsterdam is only 7 feet above sea level, so the city is always a little damp. There is high humidity in the summer and a fair amount of rain, especially in the winter, but, moisture aside, Amsterdam's weather is ultimately comfortable. The temperatures are rarely extreme, and there are lots of balmy days, especially in June, July, and August. November to April is overcast and windy with a bit of snow and ice around the New Year.
Whatever the weather, it doesn't hang about for long, so plan for every eventuality. Wear layers to put on or take off, have sturdy shoes for your explorations on foot, and bring a good umbrella.