What are the three main cruical events to know about the British empire decolonising in Africa?
The most important event to know about in this regard is World War II. World War II did not directly lead to the loss of any British territory in Africa. However, it did weaken Britain greatly. The loss of British economic and military power, and the rise of American power, made it more likely that Britain would have to decolonize.
A second important event would be the Suez Crisis. This event showed that the US would not necessarily back Britain in its attempts to retain power in Africa.
A final important event could be Harold Macmillan's "wind of change" speech in 1960. By giving this speech, Macmillan was signaling that Britain would not fight to retain its colonies in the way that France was fighting in Algeria. This helped lead to a burst of decolonization that saw most British colonies in Africa become independent within 5 years of Macmillan's speech.