How do i add two lists' elements into one list?

A solution using a loop that you try is one way, this is more beginner friendly than Xions solution.

list3 = []
for index, item in enumerate(list1):
    list3.append(list1[index] + list2[index])

This will also work for a shorter solution. Using map() and lambda, I prefer this over zip, but thats up to everyone

list3 = map(lambda x, y: str(x) + str(y), list1, list2);

You can use list comprehensions with zip:

list3 = [a + b for a, b in zip(list1, list2)]

zip produces a list of tuples by combining elements from iterables you give it. So in your case, it will return pairs of elements from list1 and list2, up to whichever is exhausted first.