Learn Russian: Если фермер пойдёт в поле, то он будет долго работать. - If the farmer goes to the field, then he will work for a long time.

In English, we use the present tense in the 'if' part of a sentence even when talking about the future ('If he goes...'). In Russian, if the action will happen in the future, you must use the future tense (пойдёт) in the Если clause.

Do I always have to use то after an если clause?

No, то (which means 'then') is optional. You could perfectly well say Если фермер пойдёт в поле, он будет долго работать. Using то just makes the connection between the condition and the result a bit stronger and sounds very natural.

Why does this sentence use two different types of future tense: пойдёт and будет работать?

This highlights the difference between perfective and imperfective verbs! Пойдёт is a perfective verb showing a single, completed action (he will make the trip to the field). Работать is imperfective because working is an ongoing process, especially since the sentence emphasizes he will do it долго (for a long time). Ongoing future actions need the helping verb будет plus the infinitive.

Why is долго placed between будет and работать?