I think what you need to do in your essay is analyze
Sylvia Plath's poetry from a feminist perspective. You might start out with several research questions:
- What roles do women play in the poems?
- How are women characterized in the poems?
- How does Plath's being a woman effect her perceptions in the poems?
- How are women treated in the poems?
- What place in society do women occupy in the poems?
- Who is the target audience of each poem?
- What is revealed about society's treatment of women in the poems?
A feminist analysis of literature involves the issues raised by the questions above. You first study the poems and determine what if anything that concerns women is present in the poems. Then you prove what you believe to be true about feminism in the poems, by supporting it with evidence from the poems.
A feminist approach to literature usually involves several issues:
- The writer as male/female.
- Roles given to women.
- Characterization of women.
- What the portrayal of women reveals about the contemporary society's attitude toward women.
Cover these and you'll be fine doing the essay.
I'll let other editors answer the rest of your question.