Our speaker is describing a fork in the road. This poem was first published in 1916, when cars were only just beginning to become prominent, so these roads in the wood are probably more like paths, not roads like we'd think of them today.
The woods are yellow, which means that it's probably fall and the leaves are turning colors.
"Diverged" is just another word for split. There's a fork in the road.
And sorry I could not travel both And be one traveler, long I stood
The speaker wants to go down both roads at once, but since it's impossible to walk down two roads at once, he has to choose one road.
The speaker is "sorry" he can't travel both roads, suggesting regret.
Because of the impossibility of traveling both roads, the speaker stands there trying to choose which path he's going to take. Because he's standing, we know that he's on foot, and not in a carriage or a car.
And looked down one as far as I could To where it bent in the undergrowth;
The speaker really wants to go down both paths – he's thinking hard about his choice. He's staring down one road, trying to see where it goes. But he can only see up to the first bend, where the undergrowth, the small plants and greenery of the woods, blocks his view.
This is where we start to think about the metaphorical meanings of this poem. If our speaker is, as we suspect, at a fork in the road of his life, and not at an actual road, he could be trying to peer into his future as far as he can. But, since he can't really predict the future, he can only see part of the path. Who knows what surprises it could hold?