AVOIR BESOIN DE
To talk about needing something (rather than having something), we use the avoir expression "avoir besoin de" (to have need of). The word "de" (of) reacts to different words near it (like "a" versus "an" in English). Here is how it works with un/une/des:
For example, j'ai besoin d'une gomme. (I have need of an eraser. / I need an eraser.)
Refer to your notes to help translate these sentences.