How to unlock a computer with BitLocker?

I'm curious, how does one go about unlocking a computer that's been secured with BitLocker? Is there a specific process or steps one needs to follow? Does it require any special tools or knowledge? And if the recovery key has been lost, is there still a way to regain access to the locked computer? I'm really interested in understanding the intricacies of this security feature and how it can be navigated in different scenarios.