According to Buddha how did we get trapped in samsara ?

First, let's define samsara.  Essentially, samsara is the continuous cycle of birth, aging, sickness, and death, which the Buddha also referred to as rebirth.  Thus, a similar question to ask is why is one reborn over and over?  What is the cause of rebirth?

When we are born into this world, into samsara, we are born with a body that contains five sensory organs of eye, ear, nose, tongue, and skin, as well as a mind that perceives and interprets their corresponding sensory experiences of sight, sound, smell, taste, and touch.  When a sense organ and a sense object come together, this is known as contact.  With the arising of contact comes instantly a feeling tone of either pleasant, unpleasant, or neutral.  This then tends to give rise to one of three mental states, which the Buddha called the Three Poisons -- greed, aversion, and delusion.  It is human nature to grasp and cling to what feels pleasant, push away and resist what feels unpleasant, and dull out or ignore what feels neutral.  Therefore, when we speak or act with a mind under the influence of greed, aversion, or delusion, we create unskillful karma.  This, in turn, continues to water the seeds of the Three Poisons in the mind, which continues to reinforce the habit patterns that create unskillful karma.  This build-up of unskillful karma is what keeps one trapped in samsara and the cycle of rebirth, aging, sickness, and death.  

An analogy that helps make this a bit more relatable is that of a campfire.  To keep a campfire burning, it needs a continuous supply of wood (or some other source of fuel).  Samsara is the fire.  Unskilful karma is the wood.  Thus, if we stop supplying the fire with wood, the fire will burn itself out.  The campfire becomes "extinguished," which is the literal definition of Nirvana -- the extinguishment of karma and freedom from samsara.  Thus by rooting out deeply conditioned greed, aversion, and delusion in the mind, we stop creating unskillful karma and cease being trapped in samsara.  

Hope this helps.  Thank you for the question.  May much peace, joy, and ease be always with you :)  

The Serpents Hand accidentally ****** some anomalous **** up and when MTF Samsara got there Samsara-2 was metaphysically expanded till she enveloped the Earth. Standard SCP stuff, didn’t you read the files?

Buddha is dead and in hell.  Before dying, he was a very fat boring man.

The serpent in the bible represents a race 

of aliens called Draconians. They set up 

a Matrix-Grid around Earth right after they 

caused the downfall of Atlantis.

Those who had retained the ancient-ways

(being to fly and teleport; living for thousands

of years); were hunted down and attacked so 

they left our planet. All who remained entered

a very deep sleep.