Wireless doorbell buttons are usually installed with two screws. They don't weigh much at all, so as long as the screws will seat into the material, it should not be a problem. Wood, vinyl, aluminum are all suitable materials to attach a doorbell button to. Brick or masonry, may require a plastic shield before you install the button.
Before you set the doorbell buttons you want to make sure you check how they are identified. One of them may be marked for the 'Front' door and one for the 'Rear'. Or they may numbered. However, they are identified you want to know where you put them before you set the chimes. Writing them down might be a good idea, especially if there are more than two.
Since there are no wires involved you are not limited on locations. You want the doorbell to be visible and easily reached. A standard mounting height is 48" above the floor. For handicapped accessible homes, 48" would be the maximum height. Often they are set slightly lower for wheelchair access.
Check the instructions, some buttons will have a base plate, allowing for battery replacement. Others will require that you have the batteries in place before you install it.