Vaisakhi has very long history relating to harvesting in the Punjab before having a significant linked to the Sikh religion. In 1699 AD, Guru Gobind Singh (the 10th Guru) chose the day of Vaisakhi at Anandpur Sahib to transform the Sikhs into ‘Khalsa Panth’ or soldier saints in the presents of thousands.

Guru Gobind Singh emerged from a tent with a sword and called out to the people if anyone would give their life away to come into the tent with him. A person came forward and went into the tent, some time later Guru Gobind Singh came out to the crowd with a blood stained sword, and asked if anyone else would come forward. Eventually, 5 people succesion came from the crowd went into the tent before Guru Gobind Singh came out with the five men, alive and well, now all wearing turbans. These five men became known as the ‘Panj Piare’ (i.e. the five beloved ones). The 5 were then baptised with holy water (or Amrit ~ immortalising nectar) by Guru Gobind Singh into the Khalsa brotherhood.
The Way it is Celebrated
Sikh temples or Gudwaras are decorated and visited. It a day were Sikh males chose to be part of the Khalsa. Singing and dancing and parades go on throughout the day