why has to be int("2")+int("3"), not just 2+3

Answer 1

"2" and "3" are strings - if you add them (concatenate) together, you will get "23" - which will still be a string.
If you want to add 2 + 3, simply add 2+3 :)
If you have strings like above and still want to add them like numbers, you have to tell Python that you want to treat them like numbers - that's what int() is for - it converts string to numbers (if the string contains digits exclusively).

Answer 2

print("2" + "3")

# outputs 23

print(int("2") + int("3"))

# outputs 5

print(2 + 3)

# outputs 5

Answer 3

a=2+3
print(a)
# it can be 2+3

Answer 4

@hosein
it can't print a
I think you meant sum
copier ;)