When your hart beats, it pumps blood round your body to give it the energy and  oxygen  it the blood moves,it pushes  against the sides of the blood  vessels  . the strength  of this pushing is your blood pressure.if your blood pressure is  too  high it put's extra strain on your  arteries  and this may lead to heart attacks  and strokes.

1)systolic pressure  :- 
                                       when your heart beats it contracts and pushes blood through the arteries to the rest of your body this force creates  pressures on the arteries is called  systolic  pressure.
2) disytolic  pressure:- 
                                          the minimum level of  blood pressure measured  between  contraction of the heart.  it may vary with age ,gender, body weight, emotional  state , and other  factor. 
blood pressure

the pressure of the blood in the circulatory system, often measured for diagnosis since it is closely related to the force and rate of the heartbeat and the diameter and elasticity of the arterial walls.

The second number, called diastolic blood pressure, measures the pressure in your blood vessels when your heart rests between beats. If the measurement reads 120 systolic and 80 diastolic, you would say "120 over 80" or write "120/80 mm/Hg