Because the staff is really a walking stick, the symbolism has to do with moving foward as you walk your path. You are on a spiritual journey and the staff will be engraved with the symbols, words, or power elements that helped you walk this path. They make up your spiritual support, your beliefs and experience.
Some traditions would require you to be initiated into some kind of priest/priestesshood. However you asked “as a green witch”, so I assume you mean as a solitary.
How to use your witch’s staff? The staff should be strong enough to support you physically, so you can use it in walking meditations, or whenever you go on hikes (as long as you take good care of it).
You can also lean on it as you ground yourself with the Earth, like another limb of your body being rooted to give/receive energy.
At the moment of using it, the staff will make you become more present and aligned to the sacred journey in which you are growing everyday.
Blessed Paths! 