Regardless of 'tradition' or 'vehicle' (yāna) chosen, there are basic ideas that underlie 'becoming a Buddhist'.Refuge and Lay PreceptsRefuge
"Taking refuge" is the basic concept that defines "becoming a Buddhist". It is not even necessary to take refuge in a formal session with a teacher, but it may help to clarify your choice and to remember your commitment. The idea behind taking refuge is that when it starts to rain, we like to find a shelter. The Buddhist shelter from the rain of problems and pain of life is threefold: the Buddha, his teachings (the Dharma), and the spiritual community (the Sangha). Taking refuge means that we have some understanding about suffering, and we have confidence that the Buddha, Dharma and Sangha (the "Three Jewels") can help us.The Three Refuges
I go to the Buddha for refuge.
I go to the Dharma for refuge.
I go to the Sangha for refuge.The Five Precepts of Lay Buddhism
The Five Precepts constitute the basic Buddhist code of ethics, undertaken by lay followers of the Buddha Gautama in the Theravada and Mahayana traditions. The Five Precepts are commitments to abstain from killing, stealing, sexual misconduct, lying and intoxication. Undertaking the five precepts is part of both lay Buddhist initiation and regular lay Buddhist devotional practices.
The Buddha is said to have taught the five precepts out of compassion, and for the betterment of society. They undertaken voluntarily rather than as commandments from a higher power. The precepts are intended to help a Buddhist live free from remorse, so that they can progress more easily on their path.
The Five Precepts:
I vow to refrain from destroying living creatures.
I vow to refrain from taking that which is not given.
I vow to refrain from sexual misconduct.
I vow to refrain from incorrect speech.
I vow to refrain from intoxicating drinks and drugs which lead to carelessness.
Renewing the vows in the Precepts and the Refuges is often a part of daily practice.
If one wishes to dedicate the whole of one's life to Buddhism and teaching Buddhism, then one 'ordains' in chosen tradition, which involves following many additional precepts.
Hope this helps.