putting separators in the chart

If I understand what you are trying to do, Excel does not have a "built in" option for adding these lines. However, you can add them yourself in various ways -- depending on chart type:

The first picture looks like a scatter chart. Adding a line to a scatter chart is as easy as adding another data series to the chart made up of one point with error bars or made up of two points connected by a line.

The second, hand-drawn picture looks like a column or bar chart. Adding lines to a column/bar chart is similar -- add another data series and change to XY scatter chart type (effectively creating a column/bar + XY scatter combination chart), then use the XY scatter data series to provide the lines.

Look over this tutorial and see how far you get: https://peltiertech.com/Excel/Charts/AddLine.html