To divide a line segment in 5, we need to measure the lenght of the segment.
Once we have the lenght we divide it by 5. This will give us the length of each of the 5 segments. Now, to divide the original segment the only thing we need to do is start on A a measure the lenght of each of the segments and put a mark on the line, then we measure again the lenght and put another mark; we repeat this process until we reach point B.
if we do this correctly then the segment AB will be divide into 5 equal segments.