We use the first conditional to say what is likely to occur when something happens now or in the future. A common question in the first conditional is "What will you do if it rains tomorrow?" You ask this question because there's a good possibility that it will rain and when it does, you want to know what your friend will do.
Remember that the "ifclause" in the first conditional has to be in the present tense, while the "result clause" has to be in the future.
1. If it rains tomorrow, I'll stay home and watch movies. 2. What do think Todd and Sarah will doif they miss their train? 3. They'll probably try to fly to Boston if they miss their train.
What about you? What will you doif it rains tomorrow?