Report on SQL created in current month

You're asking 2 questions and I'm going to assume you're either looking into or have deployed a timestamped RCM stage management system (if not, look into a timestamped RCM stage system)

creating report on SQL created in current month

The easiest way to report on SQLs per month is to create a smart list filtering SQL timestamp date = this month (or last month) and creating a monthly subscription for the smart list

How First SQL created Date is different than SQL created Date?

In a cyclical RCM model, a customer may return to a SQL if they want to purchase more things from you, or if it's a lost lead returning to SQL after going into a nurture etc... you'll then be able to tell the difference