Conditionals are used to show the results when a certain action occurs. A conditional sentence requires two clauses - the protasis (the clause that expresses the condition) and the apodosis (the clause that expresses the consequences).

Example: If you press that button, the light will shine.

The protasis may be known to either be false or highly unlikely, where a special type of conditional called a counterfactual is needed.

Example: If he were stupid, he would have failed the test.

A counterfactual can imply that both clauses are false. With the example above, one may draw the conclusion that he is not stupid, and he did not fail the test.

There are two other types of conditions. There are predictive sentences, where the consequences for a hypothetical future event are given.

Example: If I turn into a zombie, I will eat you!

There are also implicative sentences. In these if can sometimes be changed to when. These show basic facts or deductions.

Example: If/when water reaches 100 degrees, it evaporates.

Conditions can be combined with imperatives to tell someone to do something if the protasis holds true. The same can be done with questions.

Example: If you see me turning into a zombie, run!

English uses a combination of tense, aspect, mood to mark conditionals. Here are few English sentences on which you may test your conlangs' conditionals.

If I am happy, I am not sad.
If I am happy, I will not be sad.
If I were happy, I would not be sad.
If I were happy, I would not have been sad.
If I had been happy, I would not be sad.
If I had been happy, I would not have been sad.

Think about how your conlang can use conditionals holding true as conditions like (if (if A then B) then C), or other ways of layering them. How do they work with relative clauses? How do they work with different tenses, aspects and moods? What about negation? Can you give an apodosis without a protasis? Are there any irregularities in your system? It's best to read about different languages to get inspiration, as there are many things to take into account.