Im trying to install this cooktop maytag mgc7430ws, there are two brackets in it and there is absolutely nothing in the instructions about how to attach it to the cabinet

I just put one of these in. You're right, there is nothing in the instructions about this, I had to figure it out for myself.
Your kit includes two brackety-shaped steel brackets and two long screws. Look on the bottom of your cooktop, halfway between the front and back on the left and right edges and you'll see a hole on each side. They are the only holes on the bottom.
Manipulate the brackets until you see that the hole in the bracket matches the hole in the bottom AND the bracket fits upward along the side of the cooktop. The flange on the top end of the bracket goes against the bottom of the countertop.
It's useful to have another person lift each end of the cooktop while you insert the bracket from below.
Once the brackets are in lace, center the cooktop so it's straight on the countertop, then screw the brackets to the bottom of the cooktop. They will tighten against the countertop and make the cooktop stop wiggling.