Theory:

I shall be telling this with a sigh
Somewhere ages and ages hence;
Two roads diverged in a wood, and I —
I took the one less travelled by,
And that has made all the difference.
Explanation:
 
He says that in the future, with a deep breath he will say that long ago, he had reached a point in life that there were two options for him and he travelled on the road which had been travelled upon by few people and that decision made so much of difference. In the same way, when you are older, you will say that way back, when you were young, you had two options. The choice that you made, made you. This is a very powerful message for all the students - that you should be wise and be careful while making, choosing, correct alternative out of the options that you have in your life because your future depends on the choice that you make today.
 
Meanings of difficult words:
 
Numbers
Word
Meanings
1.
SighDeep breath.
2.
HenceHere, in the future.
Reference:
National Council of Educational Research and Training (2006). Beehive. The Road Not Taken - Robert Frost (pp. 15). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.