A percentage play and a percentage kick in football are statistics that measure the success rates of particular plays and kick attempts in certain situations as a percentage value. The percentage model is not entirely concrete information and doesn't apply to every situation in a football game. The percentage model is always updating, changing on every play due to a teams play calling, roster decisions, and even the weather.
For example, if a team calls the play 'curl flats' on every 3rd down and short (a 3rd down with less than three yards to go) and they are successful on converting every 3rd down and short, the success percentage for curl flats on 3rd and short is 100%. This can also be reversed, and one can claim that this particular team calls curl flats on every 3rd and short and they are successful 100% of the time, every time. Theoretically speaking, the team will always convert on 3rd and short, so long as they call curl flats. This is an obvious theoretical error in the percentage system, but it is still useful when a team is measuring their success with certain plays.
The percentage metric system can also apply to kicks in exactly the same way. A kicker makes 50% of the kicks he takes from the 40 yard line, so when given the opportunity to attempt a kick from the 40 yard line, the percentage success of that kick is 50%. Obviously, this stat can change, as the kicker can become better at kicking at this range, just as the team before can begin failing on 3rd and short. The percentage system is simply a measure of "what are the chances that this is successful?"