Explain the usage of the conjunction 'if' in a sentence.

The conjunction 'if' is used to introduce a conditional clause in a sentence. It is commonly used to express a hypothetical or uncertain situation, indicating that the outcome of the main clause depends on the condition stated in the subordinate clause.

For example:
1. "If it rains, we will stay indoors." - This sentence implies that the action of staying indoors is dependent on the condition of rain. If it does not rain, the main clause will not occur.
2. "I will go to the party if I finish my work on time." - In this sentence, the main clause of going to the party is contingent upon the completion of work on time. If the condition is not met, the action will not take place.

The conjunction 'if' can also be used to express a general truth or a habitual action. In such cases, it is often used with the present simple tense in both the conditional and main clauses.

For example:
1. "If you heat ice, it melts." - This sentence states a general truth that when ice is heated, it always melts.
2. "If I have free time, I usually read a book." - Here, the speaker is expressing a habitual action that they typically engage in when they have free time.

Overall, the conjunction 'if' is versatile and allows us to express various conditional situations, hypothetical scenarios, general truths, and habitual actions in a sentence.