For something that can happen, use if + present, then will + verb: If the bus is late, I'll walk.
If + present, then will
If the bus is late, I'll walk.
If you call me, I'll come.
Not "If the bus will be late, I'll walk." — say "If the bus is late, I'll walk.". After if, use the present, not will.
Try it: Woman: Our team is playing tonight. Man: If they ___, we'll have a party. Choose what the man says. (lose / will win / win / will lose) Answer: win — A party is for a win, so if they win; after if, use the present, not will.
The if clause second
The if clause can come second, after the main clause. Then there is no comma: I'll call you if I see her.
I'll call you if I see her.
She'll be angry if you forget.
Try it: Woman: I don't have an umbrella. Man: You'll get wet if it ___. Choose what the man says. (stops / rains / will stop / will rain) Answer: rains — Rain makes you wet, so he says if it rains; after if, use the present, not will rain.
If you don't …, you'll …
Use If you don't … to say what bad thing will happen: If you don't hurry, you'll be late.
If you don't hurry, you'll be late.
If you don't study, you won't pass the test.
Try it: Man: I'm going to bed at two in the morning. Woman: If you ___ sleep more, you'll be tired tomorrow. Choose what the woman says. (do / don't / will) Answer: don't — Two in the morning is late, so if you don't sleep more, you will be tired.
Every time: the present twice
For something that happens every time, you can use the present in both clauses: If you are cold, you put on a coat.
If you are cold, you put on a coat.
If I eat late, I don't sleep well.
Try it: Woman: Why do you take the bus to work? Man: If I ___ there, I can't find a place to park. Choose what the man says. (walk / will drive / drive / will walk) Answer: drive — A car needs a place to park, so if I drive, every time; after if, use the present.