Harmony would generally refer to the relationships of multiple notes sounded at the same time.
Texture could best be described thinking about the human sense of touch - as in smooth, silky, coarse, sharp, shrill, piercing, soft, metalic, wood, leathery, furry, etc. Musically we would use similar descriptors to describe how particular selection of music is similar to physical touch sensations.
Examples:
A picolo playing fff in it's highest register is considered shrill or even painful to some people.
One of my professors described an oboe as a "lazer". Or the more common description of "nasal."
A flute may be "silky".
Listen to Stravinsky's "Rite of Spring" there's a lot of texture in there.