The "." values are indication of a missing value. They are like having a blank in your data. When you use the JMP Platforms, they will deal with the missing values appropriately. If you want to delete the entire row where the missing values are present, you can do that by right clicking on one of the cells that has a missing value, and then clicking on "Select Matching Values". JMP will then select all rows where this column has missing values. You can then move to the column with the row numbers, hover over one of the selected rows, right click and select "delete rows".
To get rid of the "Mean(…)" I would create a new column, and then use the following formula in the new column
You can find the documentation on the Word() function in the Scripting Index
Click on "Character", because the Word() function is a function that works on character strings, and then in the right column, click on Word