You need a static IP for starters Then you need permission from your ISP to run a web server from that IP If your computer is not connected directly (router, switch etc in the way) you need to configure your computer as the default route or configure your router to send requests that come in on the ports you want to serve content from to your computer (default 80).
Next you need to register a domain and have the domain registrar's nameservers point to your IP address.
I'm trying to develop a website with ~ 200 users. the website will have a database.
1. should I have a static IP and have it the way described above OR 2. buy a domain and have the services from my ISP. I'm not sure how to have a databae of my own if I only buy a domain? I mean where will it be and how can i make sure it is secured?