How to measure Customer Retention Rate ? Cohort Analysis & Retention Rate Visualization in R

In an Ecommerce business, its important to analyze User Retention over time. Some normal questions we tend to solve-

Are the customers doing more or less repeat purchases over time? OR rate at which we are losing customers getting better or worse?

What is the overall retention rate ? How and when are users returning back after their first purchase?

Are the new customers sticking around for the second, third, fourth, .. month?