In its most basic form, a narrative has three main parts: a beginning, a middle and an end. A narrative usually resolves most of the issues the protagonist faces, but the final ending doesn't always provide closure. For example, an ending might leave the door open for a sequel. Sometimes an author wants to leave stones unturned, so a reader can create her own ending or speculate possible outcomes.
All narratives have an ending, but they don't always have resolution. Resolution occurs when story conflicts and mysteries are revealed, unraveled or addressed, and the protagonist has a personal or emotional response to them. For example, a hero finally defeats his foe, a terminally ill patient comes to grips with her mortality, or a protagonist uncovers the hidden truth behind his haunted house. Some stories have hints and bits of resolution intermixed throughout the plot, but they don't always provide a sense of closure. The English department at the University of New Mexico defines narratives as having either a closed or an open plot. With an open-plot ending, there is no final conflict resolution and the reader is left hanging; a closed plot has a definitive ending.
Resolution might occur throughout the novel, shortly after the climax, immediately before the ending or once the protagonist has a moment of inspiration. Resolution is flexible and isn't necessarily final; the characters and plot lines might even regress. Resolution can morph, adapt, re-configure, escalate or reconcile completely. On the other hand, an ending signifies "The End." Even if there's a sequel, your narrative has a definite stopping point. An ending might suggest future plot developments, but its location is clear -- always the last chapter, often the last sentence of the story.
Your characters help determine whether your story has resolution, but they don't determine whether it has an ending. Even the death of a main character doesn't mean the narrative ends there. According to professors Ron Layne and Rick Lewis from Sandhills Community College, characters must respond to the conflicts in a narrative even if there's only partial resolution, the end results are unsatisfying, or the final verdict is ambiguous. You may choose to end your narrative without resolution -- characters trapped in the middle of the jungle, learning to survive, expecting to get rescued -- but there's still an ending. It might not be a gratifying ending, but the last printed words on the page end that part of the story.
You may choose to write a narrative where resolution isn't your objective. For example, your story might be about the journey, not the destination. Or you might write about existential experiences that stress feelings and emotions over resolution. Depending on the structure of your narrative, your protagonist might remain in a perpetual state of conflict and turmoil. Even if there's no resolution, your narrative needs a purpose and an ending. Your ending might reveal something about the main character that's shocking. For example, she's experiencing everything as a patient in a mental institution, or she's already dead and is recounting her life from the grave. Or your ending might uncover a mystery such as your characters actually live in an alternate reality or exist in multiple time periods. Sometimes resolution coincides with the ending; the revelation or the "twist" might be the end to your story.