PostgreSQL Queries

I need help in writing a couple of queries to get data from a database, I'm using a visual interface connected to the db but I'm new to PostgreSQL and need some initial guidance (although I understand and can read through the code, I'm a front-end dev). This project is for two or three queries, maximum 50 lines total. Potential to be an ongoing commission/support gig. I'm not able to give you access to the database for privacy reasons but they're simple, I can explain them in a logic way with plain language. The process would be the following: 1. I describe you the columns and what I want, i.e. "I need to get the number of users who made two purchases and registered during a period of time" 2. You send me a query ready to go 3. I test it running it immediately (we can probably do this live by chat). 4. Adjustments if it doesn't work