I am trying to understand a concept that pops up in my hwk problems about friction, specifically static friction. In an example in my book, it shows that when you turn a car around a corner, you have 3 forces: normal, gravity (these cancel and are in the vertical direction) and static friction (provides the inward centripetal force to allow you to turn in a circle). However, I don't understand how static friction can exist alone as a horizontal force. I thought that static friction results in response to another force. For example, if i try to push a block, static friction force keeps it from moving. However, if the block is just sitting there, there won't be a static friction force. Can someone please explain this to me?
Also, when we walk, I understand that when I push the ground, the ground pushes back on me and that allows me to walk forward. I don't understand how friction plays into the FBD of this situation. Is friction the force of the 'ground pushing back on me'? How does friction play into Newton's third laws?