This is the correct setup of a steeltip board. The red line marks the throwing line. Height is measured from the floor to the center of the bull's eye. Note that the throwing distance is measured on the floor from the throwing line to a perpendicular line (use a plumb) from the board surface. This is not the distance from the throwing line to the wall!
To quickly check if a board is mounted at the correct height/distance you can measure the diagonal line from the throwing line to the center of the bull's eye. It is 9 ft 7 3/8in, or 293 centimeters.
If you ever play in Europe you will notice that there are softtip machines with boards sized like in steeltip. You will also find that the throwing distance sometimes is 7 ft 9 1/4 in here, and sometimes it is 8 ft...
A line on the floor you must not overstep when throwing. It can be a simple line on the floor, or a raised (wooden) bar. Such a raised bar is called "oche" (also known as "ockey, ocky, hockey..."). If you want to set up a decent throwing place you should implement an oche. You will find it in most better pubs and at all tournaments that have some importance. It just makes overstepping the throwing line impossible, leaving no room for tiresome dispute. To make it useful the oche should be about an inch high and the length should be about 2 feet or longer.
The board is sold with a clip for mounting it to the wall. On the back of the board there is a screw (at least a hole for putting a screw in should be there). This screw is placed at the center of the bull's eye and it fits in the clip. So mount the clip on the wall, at the correct throwing height. When you hang the board the screw snaps into the clip. Then fix the board with wooden chocks or cardboard. Finished.