Is there a possible way to replicate a forum software to make your own forum software? Or make a forum close to what forum software could get. A site I worked for made their own forum, but it wasn't made good. I want to see if it's possible to copy what forum software does and make your own site from scratch with how forum software sets up a forum. Or would that be impossible?
It's technically possible. You need to know a server-side programming language: PHP, ASP, Java, or server-side JavaScript configurations. Knowing XML will be important for skinning your new forum - making sure that admins can install new skins and make their own.
Knowledge of databases is important as well. You need to select the correct database for your server-side language. For PHP and Java, MySQL will be enough to store posts and display them.
Basically, when a user types a post into forum software, the textbox they are entering it into is a form. This form stores the text in a relational database, and every time the topic is loaded, the server-side language pulls the text out of the database and displays it to me and everyone else. It's a very simple programming operation. Add text to database --> retrieve text from database. Not too hard - this can be programmed with a basic knowledge of PHP (or JSP, or ASP...you get the idea).
The reason that forum software exists is because capitalism, and also because security. Security functions are getting to be too sophisticated, with too much complex math, for the average programmer to learn (do not program your own crypto, as they say). The functionality that allows me to log in with my username and password and have all of my posts associated with that name is a lot more intense than just the simple database update I mentioned. So my answer is: yes, you can try to duplicate it, but unless you have a sophisticated mathematical data scientist cryptography expert friend, your result will not be as secure as the forum software you can buy. Obviously forum software makers employ data scientists and release security patches regularly in order to make sure their customers don't get hacked into. They have money and can hire people to do that.
So my answer is: yes, but it's hard to make it secure, and you will struggle to secure your forum software without expertise or research that may take a long time to learn. If you employ your code online, you'll have to continually patch your forum yourself to stay ahead of the hackers and keep them out. This may be time you wanted to spend on other things, like creating content and dealing with your users.