Hi Fiona,
thank you for your question. Here is what I would recommend:
You can perform statistical tests with the fit Y by X platform under Analyze -> Fit Y by X.
Drag and drop your continuous variable into the Y field and your categorical one in the X field. JMP will automatically select the one way analysis.
In case you want to look at specific groups like you showed in you picture, you can apply a local data filter under the red triangle -> local data filter, select the categorical variable and filter out the groups you do not want to be included in you analysis (press control and click on the groups you want to look at).
When this is done you can look into the red triangle of the one way analysis and select the test you want to perform, like a t-test or non parametric tests.
When you need further help, just let me know.
Best,
Jonas