Buddhism is ancient religion and has evolved over time.

Guatama Buddha lived about 563 BCE to 483 BCE. He died without appointing a successor.

About 200 years after his death Buddhism split into two major schools: Theravāda (religion of the elders) and Mahāyāna (greater vehicle) -- as they are know no

The second of these two schools was to unify with Hindu Tantra and become Vajrayāna (thunderbolt or diamond vehicle)

The major resulting schools are know as

• Theravāda
  
• Mahāyāna
• Vajrayāna

In the West we primarily meet with them in the forms of

• Insight Meditation  (Theravāda)
• Japanese Zen Buddhism (Mahāyāna)
• Tibetan Buddhism (Vajrayāna)

On this website we have brief sections on each tradition. Wikipedia is always a great resource.