Some traits are found in behaviors displayed. Some of those traits are learned behaviors. For instance, a fella that always opens a door for a lady may show he is a bit of a gentleman, be old fashioned, or was taught good manners. Those are traits a writer could convey in a story with having the character do such things. Some behaviors are driven by emotion, rather than something taught. For instance, a lady who cries at the drop of a hat with or without provocation may be overly emotional. And that trait could be conveyed in varying ways throughout a story when she cries and what she cries about. To show that over emotional trait of hers. Those are just two examples. Arrogance, pride, exuberance, bubbly personality, hostility, abusiveness, etc. Those are also all behaviors/traits that lend dimension to a character and are all describable and usable in a story to make it fuller. And make your character come to life or be multidimensional.
Some traits are things that are just there in a person. For instance, a person's laugh. That is a trait that is describable. And showable in a story. A deep belly laugh, rich with tonal quality that makes others smile or laugh along. Even at a bad joke.
Some traits are found in physiology or physical appearance. For instance, a trait could be that a person has a scar or a medical condition that you use in your story that assists in defining the character and how it shapes them.
Some traits are habits. For instance, biting fingernails, smoking, drinking, etc.
Those are all traits (learned and inherent) that lend dimension to a character and are all describable and usable in a story to make it fuller. And make your character come to life or be multidimensional.
Hope I did not muddy. If I did? Iggy. Just tryin' to assist.
Good luck!
Christine