The central city of Amsterdam is not very big. It is
reasonable to walk as a means of transportation. In fact, it
is enjoyable to walk to places. It's reasonable safe
(although it's crowded, and pickpockets are supposedly a
concern; I haven't had problems yet, but take reasonable
precautions), it's pleasant walking by the canals, and it's
interesting looking at the buildings and shops. But: it can
be hard to find your way around, and you need to be bike/car
aware.
Amsterdam is like a game of Zork: A maze of twisty little passages all alike. Take a map, learn the landmarks, ask for directions. If you walk along canals, it's harder to get lost, but it's possible. I enjoy getting slightly lost: Wandering somewhere that I don't quite know, but knowing that I can get back if I walk around enough. Except the first time I did this, I confused two landmarks and walked in circles for 2 hours.
The biggest concern when walking is where to walk and crossing streets. On big streets like Damrak there are wide sidewalks and it's no problem. On the smaller canal streets, the sidewalks are often blocked and you have to walk in the streets. That's a bit more of a problem. So a few lessons in pedestrian safety and how to not look too much like a tourist.