Structure of an if condition:

if condition
  #execute logic
end
# variant
if condition
  #execute logic
else
  #execute different logic
end
# variant
if condition
  # execute logic
elsif #different condition
  # execute logic 2
else 
  # execute logic 3
end

Method code samples:

def multiply(first_number, second_number)
  first_number.to_f * second_number.to_f      
end

def divide(first_number, second_number)
  first_number.to_f / second_number.to_f      
end

def subtract(first_number, second_number)
  second_number.to_f - first_number.to_f      
end

def mod(first_number, second_number)
  first_number.to_f % second_number.to_f      
end

Branching execution code sample:

puts "What do you want to do? 1) multiply 2) divide 3) subtract 4) find remainder"
prompt = gets.chomp
puts "Enter in your first number"
first_number = gets.chomp
puts "Enter in your second number"
second_number = gets.chomp
if prompt == '1'
  puts "You have chosen to multiply #{first_number} with #{second_number}"
  result = multiply(first_number, second_number)
elsif prompt == '2'
  puts "You have chosen to divide"
  result = divide(first_number, second_number)
elsif prompt == '3'
  puts "You have chosen to subtract"
  result = subtract(first_number, second_number)
elsif prompt == '4'
  puts "You have chosen to find the remainder"
  result = mod(first_number, second_number)
else
  puts "You have made an invalid choice"
end