Where I can find a tutorial about IK?

I want to make to axe animation for(chopping trees, killing animals, etc)! Also some animations for arms! When I tried to make an axe basic chop tree animation I found a problem! The axe complete its animation through the tree because the animation position and rotation values are constant! I asked about a method to set the animation keyframes position propriety at Tree.transform.position.x, Tree.transform.position.y, Tree.transform.position.z! Someone replied and said that's impossible to change animation proprieties while game is running and also he said that I need to learn about Inverse Kinematics! I searched on YT and Google and I found tutorials about IK. The problem is that these tutorials are based about bones moving(arms, legs, etc)! And I don't understand how IK can help me in weapons motion(I didn't attached arms to my FirstPersonCharcater yet only weapons)! Please give me a very good IK tutorial or explain me how it works and what is used for!