Counterplans are advocacies that offer alternate courses of actions besides the one implied by the resolution and besides doing nothing. Coming over from policy debate, counterplans have seen a dramatic rise in popularity over the last few years and are in general used by negative debaters in expressing advocacies that conflict with the resolution. Understanding what counterplans are and what their necessary components are is a key aspect to knowing how to best respond to them.
Purpose
In reality, there are always more than two options in any given situation. Accordingly, the counterplan represents the diversity of real life choices and can be used to your advantage. If you can think of an alternative not specified by the resolution, then that would be a great time to make use of a counterplan. Further, counterplans are strategic in that you can use them to co-opt many of the benefits specified in your opponent's position without having to deal with any of the downsides (if you position your advocacy well).
The counterplan has four elements to it: the text, competition, solvency, and net benefits. Each of these sections is crucial in order to establish its legitimacy as a position and further is necessary to demonstrate the feasibility of your advocacy.
Text
The text is the section where you explicitly state your advocacy. Because counterplans very often imply evaluating an action not directly implied by the resolution, it is important to be extra specific in explaining what it is you are evaluating.
Competition
In order for a counterplan to be valid, it must be competitive. A good way to understand this is to think of competition in terms of opportunity cost. If there is an opportunity cost to taking the action specified by the resolution, your counterplan should be that opportunity cost. As long as the opportunity cost is less than the cost of the action, then you should do the counterplan instead of the plan. There are two ways to establish a basis for competition.
Further, one of the important reasons to have competition is that because the counterplan is not an advocacy directly implied by the resolution, there's no reason why the other debater can't say you should take both the course of action specified in the resolution and do the counterplan. If that is a viable option, then your counterplan is invalid.
Mutual Exclusivity
The first way to establish competition is through mutual exclusivity. What is implied by mutual exclusivity is that it is impossible to do both the counterplan and the normal course of action expressed by the resolution. This functions as a valid form of competition, as if you physically cannot do both, you are forced to choose between them.
Net Benefits
The second way to establish competition is through net benefits. The idea behind net benefits is that, regardless of your ability to do both the course of action in the resolution and the counterplan, if doing just the counterplan is strictly better doing the resolution or doing both, then the counterplan is competitive as an independent option.
As a form of competition, net benefits can be run in conjunction with mutual exclusivity but is in general the weaker form of competition.
Solvency
In order for your position to be a valid one, you need to show how you solve all of the problems that taking the normal action in the resolution solves. If your position does not in fact solve for all or at least most of the same issues, then you in general shouldn't be running this counterplan.
Note: Finding evidence on this issue is highly recommended, as this is the section that is considered most important. If you don't have strong solvency, then the other debater can treat it like any normal case and remove any strategic advantage you had.
Net Benefits
In the previous sections, you established your advocacy, showed why its competitive, and showed how you solve for most of the problems specified in your opponent's case. The net benefits section is where you take the final step and show why your position is in fact preferable to your opponents.
In general, a lot of what goes in here is very similar to the kind of information that goes in the contention section for a lot of cases, so it's important to follow the same argument style that you have been using. If you want to try framing these as disadvantages to the affirmative position, as they are formally done in policy debate, look here to see how best to do so.