Theory:

And both that morning equally lay
In leaves no step had trodden black.
Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back.
Explanation:
 
The poet says that both the paths were similar that morning. Both the paths had leaves and grass on them, and no one had stepped on them as they were still green in colour; otherwise, they would have been crushed by the foot. He thought he would take the other path for another day, although he knew that one way leads to another. He knew that he could not go back on the alternate he had taken. In the same way, in our lives, if we choose an option, we must keep on moving ahead with that option as we never get a chance to come back and take the other option that we had left earlier.
 
Meanings of difficult words:
 
Numbers
Word
Meanings
1.
Trodden Walked over.
2.
Wanted wearHad not been used.
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.