The scatter plot is a visualization used to compare two measures. More aspects of the data set can be expressed through the use of shape, color, and size within the scatter plot. Also reference lines can be added to express correlation. Scatter plots offer a good way to do ad hoc analysis.
In Tableau you create a scatter plot by placing a measure in the columns shelf and another measure in the rows shelf.
By doing this you are asking Tableau to compare two numerical values. Tableau chooses by default a scatter plot as a default visualization for this.
The first visualization of your scatter plot might not be very exciting, a single point showing the sum of all values for both measures. One way to develop your scatter plot from here is to go to Analysis and click on Aggregate measures.
Alternatively, you can bring dimensions to add detail , you can add additional measures and/or dimensions to the Rows and Columns shelves to create multiple one-mark scatter plots in the view.
Example above, adding the Category dimension to the Color mark card.
Example above, adding Category to the Shape mark card.
Finally, I leave you with a link to a really cool animated connected scatter plot.