How can I code a Gacha System in C# (With RNG)? [closed]

For my first actual game, I want to code a gacha system based off of RNG. For example:

• 5 rolls have 1 silver character
• 50 rolls guarantee a gold character
• There will be a pity system

I wanted to get the basics in, i feel like going into detail will make it less understandable. How can I code a whole gacha system with RNG that won't drain players. I use Unity and Visual Studio.