Whereas the second conditional talks about things that are unlikely or impossible to happen, the first conditional talks about things that are likely to happen in the future.
If we win the league, I will be very happy
If I buy more food, I will be very poor
If she is horrible to him, I’ll feel bad
As you can see, the first conditional usually uses the infinitive of the verb (is, buy, win), without ‘to’, and, usually, will. It can also use the present continuous tense or present perfect tense.
If she’s running, she will need water
If I’ve finished studying by 4, I’ll probably go to the cinema
Like the other conditionals, the first conditional uses a conditional and its result.
If I drink more coffee I will feel very anxious
If she travels by bus she’ll need to buy a ticket
If they’re going to the park I’ll go with them
If John has finished eating I’ll take his plate to the kitchen
The conditional is a description of a possible situation (travelling by bus, drinking more coffee) and the result is what is likely to happen if the condition is true (will need to buy a ticket, will feel very anxious).
The first conditional can also use different modal verbs to express the likelihood or ability of the result occurring:
If you contact me at 5, I might be eating, so call later
If Gerald misses the flight, he can get the later one
We can also use the imperative with the first conditional. The imperative stresses that something needs to happen. So if the condition occurs, then the result ‘must’ (according to the person saying it) happen.
If Donald speaks again, don’t interrupt him
If Gary buys the New York Jets, congratulate him