If we still find a little confusing when do we have to use the first or the second conditional, here it is a good way to see it through this link taken from youtube made by the British Council.

Remember: we use the first conditional to talk about things which might happen in the future or their consequences.

• FORM: if + present simple, ... will + infinitive
• If it rains, I won't go to the park.
• If I study today, I'll go to the party tonight.

We use the second  conditional to talk about imaginary situations.
First, we can use it to talk about things in the future that are probably not going to be true. Maybe I'm imagining some dream for example. if + past simple, ...would + infinitive

• If I won the lottery, I would buy a big house.(I probably won't win the lottery
•  We can  also use it to talk about something in the present which is impossible, because it's not true. Is that clear? Have a look at the examples:
• If I had his number, I would call him. (I don't have his number now, so it's impossible for me to call him).
• If I were you, I wouldn't go out with that man.