Compare the ARR from all customers you had 12 months ago to that same set of customers today. Expressed as a percentage, divide the ARR from those customers today by the ARR from 1 year ago.
Run Rate ARR is the annualized value of the recurring portion of all the contracts you have active on a given date. Put simply, if you add no new customers, don't lose any customers, and don't upsell any customers this would be your revenue over the next year.
The number of unique new customers that signed up for a subscription (or made a transaction) at a specific point in time, or over a time period. New logos are new customers.