What's wrong?

#You have few problems
#first,I want to explain your problem detaily.I hope you can understand it. If you have question ,ask. You can also type @Mr. love to call Mr. love to help you.
#second,you are doing good. When i was doing this code before, i can't even write that a lot as you. 
#you are very close to complete it.


#correct code
import random
def even_odd(num):
    # If % 2 is 0, the number is even.
    # Since 0 is falsey, we have to invert it with not.
    return not num % 2                                # When i was doing this code challenge, i don't know the not statement, it looks like u don't too (explaing 2.5)
start = 5
while start:                            #i will explain why removing True works(explaining1)
    ran = random.randint(1, 99)
    if even_odd(ran) != 0:                            #i switched the == sign to 1=.(explaing2)
        print("{} is even".format(ran))
    elif even_odd(ran) == 0:
        print("{} is odd".format(ran))
    start -= 1                                               #i don't think i need to explain this because ur start -=1 was under the elif statement.

#explaining1
#if u runs it in python 
>>>True ==1
True
>>>True ==5
False   #See, True is 1 ,not 5
>>>start =5
>>>start ==True
False                 #because True is 1 ,not 5. That is why start is not True or equals to True.
#Therefore, the while start True won't work.

#Here comes the HOWEVER

#when u put the start in the if statement or while statement like this ,the start will becomes True,not 5:
>>>if True:
...      print('it is True')
"it is True."
>>> if start:              #it works like if True ,although when u put start ==True, it will give u False. Tag Mr. Love to know more.             
...      print('it is True')
"it is True."
#Therefore 
#it is same when you use "while start" as "while True".
while True
while start

Explain 2

#Your code was:
    if even_odd(ran) = 0:                            #i know u want to say when even_odd(ran) equals zero ,but that is "==" sign. When u r setting like this ,u r asigning variable "even_odd(ran)" to a number zero.
        print("{} is even".format(ran))
    elif even_odd(ran)  != 0:
        print("{} is odd".format(ran))

# after changing = sign to == sign, here is how your code runs (of couse taking out the start -=1 outside of the elif statement.
>>> 
 RESTART: C:/Users/JonathanSum/AppData/Local/Programs/Python/Python35-32/t15.py 
73 is even
23 is even
26 is odd
68 is odd
74 is odd
>>> 

#You see it said 73 is even. 
#That is because u don't understand the "not" statement. I guess Mr. Love didn't explain it too.
>>> 3>2
True
>>> not 3>2
False                #it is just making things oppsite.
#That is why Mr. Love put a comment  like this:
    # If % 2 is 0, the number is even.
    # Since 0 is falsey, we have to invert it with not.
for more detail about how the odd_even function works and why having not statement in even_odd function, plz check the explaining 2.5


#reminder: even your putting a even number in even_odd function, it will give u a True or return  to True.
>>>even_odd(8):
True
>>>even_odd(5):
False
#reminder :True ==1 and False ==0


#Your code again:

    if even_odd(ran) == 0:                       #True is equal to 1 ,not zero
        print("{} is even".format(ran))
    elif even_odd(ran)  != 0:              #Now you understand why ur code gives you odd number is a even? True ==1 and False ==0
        print("{} is odd".format(ran))


Explaining 2.5(Not statement and how even_odd function works:
def even_odd(num):
    # If % 2 is 0, the number is even.
    # Since 0 is falsey, we have to invert it with not.
    return not num % 2

#Not statement,when num =100 and 100%2 =0,. That is why when u put even number into the even_odd function, it will give your zero. However, with the "not" statement, it will convert False or 0 to True.
That is how the even_odd(True_False) function work. When you put even number, it will covert 0 or False to True ,and this True ==1.