In short, a woman is battling a form of insanity (is it post-partum depression? something more serious?) on the surface of this story.
However, the real story is about women's rights and women's voices being truly heard and acknowledged--the main character's worries are brushed aside by her husband because he thinks her illness is due to her being a woman, therefore it's all in her head.
Enotes has great resources on this story. I always suggest to read the summary here if you are not understanding, and then go back and read the real story. This will help you already have an idea of where the plot is going so you're not so lost.
I also included a link to an essay Gilman wrote about why she wrote this story in the first place--gives good insight into the feminist principles which are the story's foundation.