It's a great activity to help your toddler get a bit more familiar with the letters of the alphabet and you could use it for numbers as well. Essentially all you need is some blank paper, some bingo dabbers, and a pen or marker to draw some circles on the paper. (We also used our "craft cardboard" to protect the table, and a smock) The circles don't need to be perfect by any means, but they do need to be big enough that a bingo dabber dot could comfortably fit inside it.
We tried a few letters and the boy-o caught on really quickly. I showed him how to do the first one by making a "dot" inside the circle, and that's all the instruction he needed--as off he went filling in the rest of the dots. He did a fantastic job at it, and was really focusing to make sure his "dots" were right inside the circles. After doing a few letters I just gave him a totally blank page to let him have at it and let his creative ideas flow.