Hello everyone i am going to be building my very first PC for the first time and i am very nervous because i don't want to break any parts so i have looked on youtube for tutorials and i understand everything apart from the power supply cables, theres like 1000 cables coming off the power supply, what will happen if i forget to plug one of the cables in? Will this break the system? or will that part just not work?
Not all of the cables coming out of the power supply necessarily need to be plugged in. Better to think about the other way around: think about what parts in your PC need power from the power supply. Parts that aren't getting power simply won't work, which usually means your computer won't boot up (parts won't get damaged by not being plugged in).
Do you already have a power supply you're working with? If not, you might consider buying a "fully modular" unit which doesn't have any cables coming out of the back: you plug in only the cables you need to both the component and the PSU, which is less confusing the easier to do cable management with.
Don't panic they're actually fewer than they look.
If you don't plug in something to the power supply it won't get any power and thus won't work. No harm done. Just switch off at the wall, plug and play.