Here's an example of a hand-drawn frame for "The Little Mermaid.":
Traditional hand-drawn animation was extremely common back in the early 20th century, and it was very difficult to master. In order to make the illuion of movement look smooth and connected, animators had to drawn frame by frame of the objects they were animating. This usually resulted in thousands of frames being needed to just for a handful of scenes. This was an a very time consuming process, and this is one of the main reasons it would slowly die out within the decades to come. But it is still used in modern media in some cases today.
Some examples of classic hand-drawn animated media include: