Im a bit tired right now so ill throw you a source and try to explain.

Penal excess and surplus meaning : public torture lynchings in twentieth-century America - Garland, David. In: Law & society review [2005]

Basically there were 3 types of lynchings. You had private lynchings, these were ones where a few men would find and kill a black man/woman who was guilty of some sort of crime, this kind of lynching was often pre-mediated and planned in advance as a sort of personal vendetta, no publicity included.

Then there as the posse lynch most popularized by the KKK where a mid to large group would find and kill a certain black for transgressions, most often economic or political. These deaths would not be publicized during the event but rather after being found by a passerby the morning after.

Then there is the Mob lynchings. These ones are the ones you are most likely talking about. These occurred during widely publicized events i.e. blacks accused of rape were being kept in a sheriff/police cell. These were often not pre-mediated but rather occurred as an explosion of public sentiment (i have heard it said that lynchings were the release valve of some Southern states) and occurred more often than not spontaneously. The mob would gather outside the black's residence or place of incarceration then at some point or another enter and carry the black out. He/she would then be over the course of several hours tortured by various means often including disembowelment with the participants parading around with the lynchee's organs, being cut up slowly with knives, being tarred and feathered, being castrated etc. The various methods used were often different and dependent on gender (a white man has been recorded as being mob lynched at one point) however there was an underlying similarity. Each lynching was very ritual in how it was done following a basic time-line (like following a cookbook) with many people children included participating. Vendors would set up stalls to sell various foodstuffs, photographers would take pictures and sell them as postcards etc. In the end the lynchee would die and often be dismembered or hung and left there. The media was often present and would give a running commentary during the whole event.

There is a few things i have forgotten but that should cover it i hope

To describe it simply it was very much like a very disgusting (for this generation) community bonding session over some torture and death.

EDIT: Photo collection of some lynchings http://withoutsanctuary.org/