This sort of question can land into different type of scenarios and so is good to clear which are the possible situations in order to have the proper answer.

+ In case you want to put variables across the top one after each other, to create a sort of 'banner', you can do this by simply select all the variables you want there and click on 'Add across' button.

Alternatively you can create a Target Group that define the 'banner', and use it 'across the top'

+ In case you want to create a 'banner' which is on 2 levels across the top, you have 2 cases:

    1. 1 variable across the top, and a list of variables/targetgroup across but nested. You can do this by adding the main variable across the top and the other 'across the top nested'. About the other if you want them to appear in one single line below the main variable, you need to create a Target group with those variable and put the group 'across the top nested'. If you want the other variables to be nested but instead of being in one line, to be one below each other (nested), you need to add them across nested, in the desired order .
    2. 1 list of variable across the top 'banner' (which can also be a pre-created target group) and a variable across nested. This is also possible, the table is correctly created in DataDynamic, but in most cases the number of headers increase considerably and complications can rise when trying to find a proper chart template. For such reason, since most of the times tables are produced to generate a chart, we recommend to design your table following the criteria highlighted at point 1).