seismic refraction method basic studies

i am a geology undergraduate student having least knowledge in geophysics ..

can anyone help me ..

In seismic refraction studies how to interpret the received signal in geophone (i.e the vibration due to shock waves )
if a seismic source is bombarded a wave will travel in all directions, if so the wave which makes a horizontal path should reach the geophone before the refracted waves but it is not like so (the refracted waves only reaches the geophone) ..the reason behind it can`t be understood properly..
on the other hand how to determine the depth of the layer .
how to determine the refracted ray path ..