The four types of conditional sentences are zero, first, second and third conditionals.
Zero conditionals are sentences that express a general truth. We use them to talk about our experiences and knowledge that we know to be true. They are often formed using the present simple verb tense. For example: "If you heat ice, it melts."
First conditionals are sentences that express a possible future event or situation, depending on certain conditions being met. They are often formed using the present simple and future simple verb tenses. For example: "If it rains, I'll stay home."
Second conditionals are sentences that express an imaginary future event or situation, that is, something that is unlikely to happen. They are often formed using the past simple and would + verb. For example: "If I won the lottery, I would buy a house."
Third conditionals are sentences that express a hypothetical past event or situation, that is, something that didn't happen in the past and can't be changed. They are often formed using the past perfect and would + have + past participle. For example: "If I had left earlier, I wouldn't have been late."