oh dear. i am sorry. i just realized that i need a shift register and not a decoder.
a decoder would be a good way to reduce many pins to few, but i would only be able to control one of the output pins at a time. so this would be great if i wanted to light up one led at a time in the matrix. but if i ever wanted to light up multiple ones, im gonna need a shift register. and i just realized why.
learning
thank you all