Try this:
1. Choose Summary Table from the Insert menu.
2. Drag a numeric attribute name (e.g., age) to the top area of the table (the blank rectangle the arrow points to, under the words Summary Table).
3. Choose Add Formula from the Summary menu. The formula editor opens.
4. Enter median( ). Do not put anything in the parentheses!
5. Close the formula editor. You'll see something like this:
You can add more functions and more variables.
If you add a categorical attribute, e.g., sex, you get a count by default instead of the mean. You can still add formulas, to get something like this: