Slides can have many animations, so it can be annoying to test them if you have to start from the very beginning again.
Fortunately you can choose the starting point in the animation list just by clicking on the item and clicking on the Play from button at the top op the task pane.
You can also make a selection of consecutive animations by clicking on the first one and pressing shift+click on the last one. Then click Play selected at the top of the animation pane.
The same thing can be done with non consecutive animations. Just ctrl+click to select the animations and click Play selected.