Build a cohort retention analysis

Build a cohort retention analysis from my data [link or upload of signups plus activity or orders]. Group users into monthly cohorts by signup month, then compute the percentage still active in each following month. Lay it out as a retention triangle (cohorts down the side, months across the top), add an average retention curve, and call out where the steepest drop-off happens. Summarize what the curve implies about onboarding versus long-term stickiness. Put the triangle and chart in a Google Sheet and the writeup in a Doc.