How do I compare two periods?

Use the Total view of the P&L, the view it opens on. It puts your range beside the period of the same length just before it. Say you look at 1 to 20 August. The P&L then compares it with 12 to 31 July, which is also 20 days. You set the range in the P&L's range picker.

The table then has four columns: Line, your range, the period before it, and Change. Change shows how much each line moved, like +12,5%. For a percentage line, it shows the difference in points, like +1,2 pp. So going from 20,0% to 21,2% is +1,2 pp. Green means better and red means worse. Grey means it barely moved, or that the line is neither good nor bad, like Taxes.

The strip under the chart at the top of the P&L shows the same comparison for five figures. This KPI strip puts a chip with the change beside each total.

To compare more than two periods, use the Daily, Weekly, Monthly or Yearly view. Those put one column per period, side by side. Either way you compare the same lines, so you can always find the line behind a change.