How do i detect the player's speed?

You have x y and z velocity procedure blocks for this

I suggest you check our tutorials collection playlist on our YouTube channel which contains many examples and tutorials that can help you get started with MCreator: https://www.youtube.com/playlist?list=PLAeL-oIFIEngE6jRgFYeFMfuj8WQsO3Ei

this procedure blocks don't exist anymore... or I don't see them

so, thery is another way to get the player speed? (and set)

Yeah they don't exist anymore. they were replaced by delta movement blocks (which are inconsistent and broken). but you can get the walk speed parameter maybe? There is also a "Is (target) sprinting" block which you can send a message in chat when true.