Human minds love to ask 'how?'   That question, when answered, helps us to understand the mechanism of an event and makes us feel that everything is under control.  When Jesus died on the cross, Luke, the physician, does not try to explain how everything happened.  He simply describes the eye-witness accounts factually and briefly (Luke 1:1-4).
 
The drama was clear.  After only three hours on the cross (Mark 15:25), the sun stopped shining.  It was dark from noon until 3.00pm.  The darkness symbolised the sin of the world which Jesus had chosen to bear for all of us (2 Corinthians 5:21).  At the same time, the heavy curtain separating the Holy Place from the Most Holy Place in the temple was ripped open from top to bottom (Mark 15:38), exposing the place where God promised to be present.  The temple curtain had been the divinely designed barrier to prevent unholy people even seeing the Most Holy Place (Exodus 26:30-33; Hebrews 9:1-4).  Only the High Priest was allowed there once a year, and only with an atoning sacrifice for his sins and for the people’s.  When Jesus died, the curtain was no longer necessary because the sacrifice of Jesus enables free access to God for all who believe in Jesus as their mediator (1 Timothy 2:5-6).

Then Jesus voluntarily surrendered His spirit to Father God.  His loud cry simply announced that His life was not taken from Him but He laid it down of His own accord (John 10:18). His breathing stopped because His body was dead.  
 
There is no need for us to ask 'how?'  This was no scientific experiment to be understood and replicated.  The death of Jesus Christ was unique and unrepeatable.  A better question is 'why?'   The answer is in Hebrews 9:28: "Christ was sacrificed once to take away the sins of many; and he will appear a second time, not to bear sin, but to bring salvation to those who are waiting for him."  Those who embrace His sacrifice as a substitute punishment for all their sins will live in eager expectation of His return.  On that day He will personally welcome them, completing the work of salvation as they are finally removed from the gravity of a sinful nature and orbiting temptations.  All others have no such assurance.  So if you are trusting in His death for you - live like you mean it!  And tell your friends and colleagues while there is time.