3 ways for doing this.
Simplest way: use the basic material editor, and in the transparency slot, load in your transmap.
Hard way1: in the advanced mat editor, right click the colour production function, then in the function editr, add a texrture map input node, load in your transmap, and connect the node to the alpha output.
Hard way2: advanced mat editor, transparency tab, se transparency to 100% and check variable transparency. Right click the transparency production sphere, and connect your transmap to the transparency output.