This is what I learned about Newton's first law of motion. He developed it in his book Principia and it states that every object at rest stays at rest and every object in motion stays in motion until an unbalanced force acts upon the object. If this happens, the object accelerates and its motion can change in every imaginable way. If the forces that act upon an object are in balance, the object is in equilibrium. (don't mistake: That does not mean that the object is at rest.) If this is the case, the forces that acting on the object at the x and y axis have to equal zero. If a force is applied at an angle, we have to use the vector component method to solve for the x and y components. What I have found difficult was the equilibrium part, because for me it is easy to mistake being in equilibrium with being at rest. My problem solving skills improved, because I learned how to draw FBD's and how to name different types of forces. But I still make mistakes, because I still like to skip parts of the problem solving method. Further I did not do too good on the parts, where I had to mark the system a force is acting on.
Newton's laws are acting all around me in the world. I literally go around, thinking about gravitational force and tension force on my backpack and how they balance each other. Learning about Newton's laws is one of my favorite Physics parts and I enjoyed our practical experiments. Further I look at sports from another point of view. Newtons first law affects everything from soccer over football to dancing. I started reading parts of Newton's principia and found the following video on youtube (thx). I hope you have fun with this. Julius