There are three types of "If..Then..." Clause. 2 of these uses "would"
Let me try to explain all of them -
Notice that the word "then" may not be actually there. It can be implied e.g. - "If I reach the market in time, [then] I will bring milk.
1.If <Present tense>, then "will + base form of verb"
e.g. If he practices hard, he will win the championship
2.If <Past tense>, then "would/could + base form of verb"
e.g. If he practiced hard, he would win the chamionship
3. If <Past Perfect tense>, then "would/could have + past participle form of verb"
e.g. If he had practiced hard, he would have won the championship
Also note that this list of "would" usage is not exhaustive but a frequently used one.
Lastly, one more usage of if..then clause -
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