Short questions without context are best answered by searching the web. If you have a more specific question that is not amenable to be answered by searching the web, give us some background on what you are trying to achieve, tell us what you know already, what you have tried, what you have found on the web and why it wasn't satisfactory… something!

BIOS will start the PC for you, and give you the control. You still can use routines offered by BIOS after BIOS gives you the control, but you need to stay in the same mode of the CPU in order for the calls to work directly. CPU has various modes of execution. Intel has basically 16+32(real mode, the mode of BIOS), 32 and 64 bits modes(plus Virtual Machine modes and a secret SMM mode you can not even peek at).

The things BIOS does to the hardware when its routines are called are still valid in any mode, but the routine itself will not execute if it is in different CPU mode.

You can keep using BIOS or abandon it. It is up to you.

Newer OSes often use UEFI.

Extra help for you:
https://en.wikipedia.org/wiki/Advanced_Configuration_and_Power_Interface

I'm telling you what to do if you want to get better answers from this community. Feel free to ignore me, but then I won't answer your questions, and I suspect many others here will do the same. NikiTo seems to not have the same demands I do, but eventually everyone gets tired of being used as a replacement for Google.

@alvaro My head hurts, so i distract myself from thinking about the pain. Can not open my coding spaghetti right now. This is the reason i answered.

I agree people should explore other options like Google, before asking.

(…and even more important - be kinder to the ones who answered)

BIOS has its own drivers.
The OS will switch to its own drivers because they are more advanced than the drivers of BIOS.