Is there a tutorial or something like that ? https://kb.speeddemosarchive.com/Super_Mario_64_DS this is the only thing that i could find

The SDA knowledge base is very outdated and there's no tutorial. I never really bothered to make any tutorials or to update the KB as I thought this game would never be very popular so it would be pointless, although if it gets launched on wii-u VC I could definitely see it growing a bit.

It really depends which category you want to do. 80 star shouldn't be too difficult to learn just by watching mine or fox's run. For 50/8/1 you might get stuck on a few skips so feel free to ask about them. 150 is probably the hardest to learn right now as there's no solid run videos out there (and I'm probably not a ton of help there as I have only done it a few times without learning/practising it).