Even though I walk through the valley of the shadow of death,
I will fear no evil,
for you are with me;
your rod and your staff,
they comfort me.
Understanding the emotion of fear: Fear is like walking in a valley and all around you is shadows, but the shadows aren't just dark, they are death shadows. Death all around. That's a situation where most people would experience fear.
Bible understanding: When I am scared, God comforts me, in the same way that a shepherd would comfort a sheep in a scary valley of death (and sheep are easily scared). A shepherd comforts his sheep with his rod and staff, which are used to guide the sheep in the way to go, and also to defend the sheep from attacking enemies. God guides and defends his people when we are experiencing fears.