The idea of writing a thesis for a poetry essay escapes me. I don't understand it at all. Can somebody please break it sown for me in easy to understand terms?

A thesis statement introduces the reader your topic and main argument, often in 1-4 sentences. There's nothing inherently different between a thesis about a poetry essay or any other form of literature: A thesis should outline the main claim/idea you're setting out to explain, the direction of your essay.
As you read the poem, make notes of any questions that arise or things that seem curious or interesting. There are no rules (outside your assignment) governing what kind of question you should ask. It's helpful to focus on answering one specific question rather than exploring an array of vague ideas.
Here are some things to ask yourself if you can't come up with a question you like:
What kind of language is Frost using, and what effect does this have on the reader?
What's the form of the poem? Does it help or hinder the readers perception of the text?
Are there any references or allusions Frost is making that help explain something about the poem?
What's the tone of the poem? Does it change?
Once you've decided on a question to focus on, restate it as an answer or statement. For example: "What is the significance of figurative language in 'The Road Not Traveled?'" becomes "In 'The Road Less Traveled,' Robert Frost employs metaphor instead of simile to make the reader feel..."
Your thesis will often change as you work through your essay, so don't worry about getting it perfect from the start.

The idea of a thesis statement is to give an introduction to your essay and offer a quick insight into your overall opinion and/or conclusion. The thesis should be one or two sentences long and summarize the essay.
Writing a thesis for a poetry essay is no different from a thesis that would accompany a longer text, whether you're exploring a broad scope of work—for example, the poetry of Robert Frost—or a single poem.
It helps many students to ask themselves a question about the subject, usually about the thing that strikes them as most interesting or research-worthy. It can concern the theme or style or both. The thesis will then take the form of an answer. For example, if you're reading a poem that is very crude and possibly offensive, the question might be, "Why is that?"
The thesis could then be something like this, broadly phrased:
The poet uses provocative language to draw the reader's attention to a hurtful topic and illustrate the need to express their anger.
Or maybe the poem is very comparison-heavy, seemingly over-explaining a simple theme. You could ask, "Is the poet overdoing it?" Depending on your point of view, you could answer with a thesis:
The poem uses various imagery to transport the reader into the poet's own childhood, trying to capture the sense of melancholy and nostalgia.
The question doesn't even need to be your own. The type of poetry usually chosen as the topic of an essay has usually stood the test of time and has something universal to say. That in itself is enough of a question—why has this particular poem or body of poetry proved so timeless?