Theory:

It was only when I began to learn that my boyhood freedom was an illusion, when I discovered as a young man that my freedom had already been taken from me, that I began to hunger for it. At first, as a student, I wanted freedom only for myself, the transitory freedoms of being able to stay out at night, read what I pleased and go where I chose. Later, as a young man in Johannesburg, I yearned for the basic and honourable freedoms of achieving my potential, of earning my keep, of marrying and having a family — the freedom not to be obstructed in a lawful life.

Explanation:

 

Only when he realised that his youth independence was a mirage, he realised as a young man that his freedom had already been taken away and he begin to crave for it. As a student, he wanted just temporary freedoms like being allowed to stay out late at night, read whatever he wanted, and go wherever he pleased. Later, as a young man in Johannesburg, he ached for the basic and honourable freedoms of realising his potential, making a living, marrying and starting a family – the right to live a lawful life without being blocked.

 

Meanings of difficult words:
 
Sl. No
Words
Meanings
1
ValleyA low area of land between hills or mountains, typically with a river or stream flowing through it
2
CrestThe top of a mountain or hill
3
RipeHaving arrived at the fitting stage or time for a particular action or purpose
4
DownpourA heavy fall of rain
5
ShowerA brief and usually light fall of rain, hail, sleet, or snow
6
IntimatelyIn a way that involves detailed knowledge
Reference:

National Council of Educational Research and Training (2007). First Flight. Nelson Mandela: A Long Walk to Freedom - Nelson Rolihlahla Mandela (pp. 16 - 23). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi..