Readers can assume from the poem's title that the "you" being addressed in this opening line (an example of apostrophe) is the speaker's daughter, and that she is about to move out of the speaker's home for the first time.
The fact that the daughter is about to strike out on her own prompts the speaker to remember another time, years earlier, when the daughter similarly demonstrated her independence, albeit on a smaller scale: when she first learned to ride a bike at age eight.
Pay close attention to what actually happens in this memory. The speaker doesn't physically help the daughter balance on the bike even though the young girl is "wobbl[ing]" as she rides. Instead, the speaker simply stays nearby, "loping along" without steadying the daughter.
This is important because it suggests that the speaker wants to give the daughter space to learn how to do this by herself. After all, if the speaker physically helped the daughter balance, then the daughter would never figure out how to balance on her own. In turn, these opening lines demonstrate the fact that granting children a certain amount of independence is an important part of childhood.
The speaker's tone is contemplative and somewhat emotional. This is made evident by the caesura in line 3, as the speaker pauses briefly before thinking more specifically about what it was like to stand by the daughter while she learned to ride a bike on her own:
a bicycle, || loping along
The pause between the words "bicycle" and "loping" draws attention to the speaker's nostalgic tone, giving the poem a slow, thoughtful sound that suggests the speaker is melancholy because the daughter is about to leave home.
The poem doesn't have a set meter or rhyme scheme, instead relying on enjambment to create its rhythm. The speaker stretches single phrases over multiple lines, creating a sensation of forward momentum that evokes the feeling of the speaker's daughter moving further and further away. The reader is pulled down the page, just as the daughter is pulled forward on her bicycle.