how do create a graph of total signups (cumulative) and signups per day?

Hello Karla,

You can use the “formula” option in the segmentation chart and use a regular formula (such as “Totals” assigned to your signup event) with a second “CUMSUM” formula (assigned to “Totals(signup event)”) which will compute the cumulative sum of your total signups. 
 
Here is an exemple I made with Amplitude demo: https://analytics.amplitude.com/demo/chart/new/ilmz8vx?source=copy+url

The only issue is that you can only use the “line chart” option to get a similar result to your graph, and both your daily/weekly/monthly/quarterly signups and cumulative signups will share the same axis scales. 

Hope this helps! 😁