In O. Henry's classic short story "The Gift of the Magi," the fact that the young couple is very poor is absolutely integral to the plot of the narrative. At the beginning of the story, Della is so despairing about the fact that she has only one dollar and eighty-seven cents that she falls down onto the bed and cries.
Her husband, Jim, more properly James Dillingham Young, was originally being paid $30 a week when he moved into the apartment the two share. Now, he feels that his name is too long for him, as he is being paid only $20 a week. You can find this information early in the story, in the fifth paragraph.
Della doesn't seem to have a job of her own. Presumably she is given housekeeping money out of Jim's $20 weekly wage; it is stated that she has put aside her pennies for savings by being careful with the meat she buys. This indicates that, as was usual at the time of this story being written, she is a housewife and is mainly occupied with the upkeep of the couple's home.