Picture this You're building a simple app. It checks if someone is old enough to sign up. Sounds easy. You have their age. You know the minimum age. You just need the program to say yes or no. But you don't know how to make the program choose. Right now your code just runs top to bottom, every line, every time. It doesn't skip anything. It doesn't branch. It has no judgment. That changes today. The ability to make decisions is what separates a real program from a list of instructions. Without it, every program would do the exact same thing every single time, no matter what. No reactions. No logic. No intelligence. If/else is how you give your code judgment. An if statement says: check this condition. If it's true, run this code. If it's not true, skip it. That's really all it is. age = 20 if age >= 18: print("You can sign up") Output: You can sign up Now change age to 15 and run it again. age = 15 if age >= 18: print("You can sign up") Output: Nothing. The condition was false so Python skipped the whole block. if age >= 18: print("You can sign up") if is the keyword that starts a decision. age >= 18 is the condition. Python checks this. It becomes either True or False. The colon : at the end of the if line is required. Forget it and you get an error. print("You can sign up") is indented with 4 spaces. This is the block of code that runs when the condition is true. The indentation is how Python knows which code belongs to the if. This is important. Python uses indentation to understand structure. Not brackets, not semicolons, spaces. If your indentation is wrong, your code either crashes or does the wrong thing. What if you want something to happen when the condition is false too? age = 15 if age >= 18: print("You can sign up") else: print("Sorry, you need to be 18 or older") Output: Sorry, you need to be 18 or older else catches everything the if didn't. It runs when the condition is false. No condition needed for else, it's the default path. Change age to 25. The if runs, the else gets skipped. Change it to 10. The if gets skipped, the else runs. The two blocks are mutually exclusive. Only one ever runs. Sometimes two options aren't enough. score = 72 if score >= 90: print("Grade: A") elif score >= 80: print("Grade: B") elif score >= 70: print("Grade: C") elif score >= 60: print("Grade: D") else: print("Grade: F") Output: Grade: C elif means "else if." It gives you additional conditions to check after the first one fails. Python checks from top to bottom and stops at the first true condition. Score is 72. Is it 90 or above? No. Is it 80 or above? No. Is it 70 or above? Yes. Print "Grade: C." Stop. The remaining elif and the else are ignored. This is why order matters. If you put score >= 60 first, a score of 95 would print "Grade: D" because 95 is also above 60 and Python would stop there. Try flipping the order and see what happens. Breaking things on purpose is one of the best ways to understand how they work. You've seen >= already. Here are all the ways you can compare things. a = 10 b = 3 print(a == b) # equal to: False print(a != b) # not equal to: True print(a > b) # greater than: True print(a = b) # greater than or equal to: True print(a = 18 and has_id: print("Come on in") else: print("Can't let you in") Output: Come on in and requires both conditions to be true. If either one is false, the whole thing is false. What if either condition being true is enough? is_member = False has_coupon = True if is_member or has_coupon: print("You get a discount") else: print("Full price for you") Output: You get a discount or only needs one condition to be true. And not flips a boolean. not True becomes False. not False becomes True. is_raining = False if not is_raining: print("Good day for a walk") Output: Good day for a walk You can put if statements inside other if statements. This is called nesting. age = 20 has_ticket = True if age >= 18: if has_ticket: print("Enjoy the show") else: print("You need a ticket") else: print("Must be 18 or older") Output: Enjoy the show Each level of nesting gets another level of indentation. Works fine, but don't go too deep. After three or four levels it becomes hard to read. You'll learn cleaner ways to handle complex conditions as you go. Let's build something slightly more real. A simple login check. correct_username = "alex123" correct_password = "python2024" username = "alex123" password = "wrongpassword" if username == correct_username and password == correct_password: print("Login successful. Welcome back!") elif username == correct_username and password != correct_password: print("Wrong password. Try again.") else: print("Username not found.") Output: Wrong password. Try again. Change the password to "python2024" and run again. Now try a completely wrong username. See how each path behaves differently. Mistake 1: Using = instead of == inside a condition age = 25 if age = 18: # wrong print("Adult") Error: SyntaxError: invalid syntax Inside an if condition, you almost never want =. You want == to compare. if age == 18: # correct print("Exactly 18") Mistake 2: Missing the colon if age >= 18 # wrong, no colon print("Adult") Error: SyntaxError: expected ':' Every if, elif, and else line ends with a colon. No exceptions. Mistake 3: Wrong indentation if age >= 18: print("Adult") # wrong, not indented Error: IndentationError: expected an indented block after 'if' statement The code inside an if block must be indented. Four spaces is the standard. VS Code will do this automatically when you press enter after a colon. Create a file called decisions.py. Write a program that acts as a basic ticket pricing system. Store a person's age in a variable. Then print their ticket price based on these rules: Under 5 years old: free 5 to 12 years old: half price (pick any price you want) 13 to 17: student price (a bit more) 18 to 64: full adult price 65 and above: senior discount Print a message that says the category and the price. Something like "Child ticket: 200 rupees" or whatever makes sense. Then change the age variable to five different ages and make sure each one prints the right thing. Hint: you need elif for this. Multiple conditions, in the right order. Your code can make decisions now. But right now it only makes that decision once. What if you want it to repeat something a hundred times without writing it a hundred times? That's what loops do, and that's the next post.