The Attack sliders - or drawbars, to give them the correct name - add an extra sound in the form of a percussive 'ping', at the footage indicated on the drawbar. You won't use them on their own, but with the ordinary drawbars. A typical jazz organ drawbar setting would be 88 8000 000 on the normal drawbars (that's 16', 5 1/3' and 8'), plus either the 4' or 2 2/3' attack drawbar.
As for First and Each, these determine how the percussive 'ping' is keyed. 'First' means that the ping is keyed on the first note played and will die away. If you play legato, the ping will not sound on the following notes. Release the keys and the ping will sound on the next note played. This is how the original percussion worked on the Hammond B-3 and M-3 organs. 'Each' means the percussion ping will sound on every note played.
Anyone using the Organ Flutes would do well to do a bit of research on Hammond Drawbars and Leslie Speakers. Or they could always learn an awful lot more in an hour by taking a Zoom lesson with me!

I've been playing Hammond (and every other major make of organ) for almost 51 years!