this is my first time brewing and im brewing a milk stout from extract i followed directions to a T but so far it doesnt say any thing about adding the maltodextrin
Dissolve it in some water and add it to the fermenter. It is mostly unfermentable, so it really doesn't matter when it is added. You might need to heat it to dissolve it. Should cool it before adding, but if it is only a couple of pints into 40 (5 gallons), the bulk temperature will only go up 1 degree for every 20 the dextrin mix is above it, so if you only cool it to 100 degrees, the bulk temperature will only go up 2 degrees and not cause a problem.