It's usual to say that we take birth by birth into different species based on our Karm and desires until one gets Moksha. After Moksha one will not take any more births.
This makes us think When, Why and How soul make entry for the first time into this cycle of birth and death? So after entry into this cycle the soul is taking different birth based on Karma and Desires etc.
We talk about getting out from this cycle of birth and death, we call this as Moksha or Liberation.
But what about entry into this cycle? Why, How and When does this happen?