There are good step by step YouTube videos by many popular creators like Linus Tech Tips. Watch few of them.
It might feel intimidating at first but it is very simple. There are 6-7 parts and you have to fit them together and put them in a box. I'll write in brief here so that you don't feel lost while watching the videos.
The parts are as follows -
1. Motherboard - Helps CPU, RAM, GPU etc talk with eachother.
2. Processor (CPU) - does all the calculations/computations.
3. RAM - Working memory.
4. Graphic Card (GPU) - Gives video signal to monitor.
5. Storage (hard disk/solid state drive) - where you keep photos, videos games and homework folders.
6. Power Supply (PSU) - Provide power to all these components.
7. Case/Cabinet - Holds everything inside it.
You need to put Processor, RAM Motherboard. Done with 3 parts.
Then you need to put this thing inside case.
Then put GPU.
Connect Hard Disk to motherboard. Connect PSU to motherboard. And done.
This is just to give you an overall idea. The sequence can be changed. Watch the videos. You can start with
this one.