To talk about a real future possibility, use if + the present form, then will + the base verb for the result. The tricky part: after if, use the present form, not will, even though you mean the future.
if + present, even about the future
If it rains tomorrow, we will stay home.
If I see her, I will tell her.
If you study hard, you will pass.
Not "If it will rain, we will stay home." — say "If it rains, we will stay home.". After if, use the present form (rains), not "will rain".
Try it: If I ___ time tomorrow, I'll help you move. (have / will have / had) Answer: have — After if, use the present form, even for the future: If I have time. "Will have" puts will in the wrong half (it belongs with the result), and "had" is for an imaginary situation, not a real future plan.
The result half uses will
The result is where will belongs: will + the base verb. (You can also use can, may, or might here.)
If you don't hurry, you will miss the train.
If we save money, we will buy a car.
She will be angry if you're late.
Try it: If we leave now, we ___ the early train. (will catch / catch / caught) Answer: will catch — This is one specific future plan, so the result half uses will + the base verb: we will catch it. "Catch" with no will would sound like a general always-true fact, and "caught" is the past, not a future result. (Note: the if half keeps the present, leave, but the result takes will.)
Either half can come first
You can put either half first, and the meaning stays the same. When the if half comes first, put a comma after it. When the result comes first, use no comma.
If you ask, I will help.
I will help if you ask.
If it's sunny, we will go out.
Try it: Which one is punctuated correctly? (If it's sunny, we will go out. / If it's sunny we will go out. / We will go out, if it's sunny.) Answer: If it's sunny, we will go out. — When the if half comes first, put a comma after it: If it's sunny, we will go out. The second option forgets that comma, and the third adds a comma where none is needed (no comma when the if half comes second).
Asking a first-conditional question
To ask about a real future situation, put the question in the result half: Will + subject + base verb, plus the if half. Or start with a question word: What will you do if...? The if half still keeps the present form. For a negative result, use won't: If you don't hurry, you won't catch it.
Will you call me if you need help?
What will you do if it rains?
Where will we go if the shop is closed?
Not "What will you do if it will rain?" — say "What will you do if it rains?". Even in a question, the if half stays present (rains); will goes with the result half only.
Try it: ___ you wait if the bus is late? (Will / Do / Are) Answer: Will — A first-conditional question puts will in the result half: Will you wait...? The if half keeps the present form (is late). "Do you wait" asks about a habit, not one real future situation, and "Are you wait" is not a possible verb form.