what is the meaning of str in line 4 ?

Question

elif user_input == "add":
num1 = float(input("Enter a number: "))
num2 = float(input("Enter another number: "))
result = str(num1 + num2)
print("The answer is " + result)

Answer 1

str-string.. On line four your getting num1+num2,converting it into a string then assigning it to result..

Answer 2

why can we directly assign float valve to result ??