Very basic Hangman game in Python
Brand new to programming myself, but here's what I've got for you.

This is just different formatting to not call print so many times:

def printOutVictory():
    print('You won!')
    print('The word was ', theWord)
    print('Press enter to quit...')


Alternate format:

# snake_case over camelCase in python
def print_out_victory(): 
    message = "You won!\nThe word was " + theWord
    message += "\nPress enter to quit..."
    print(message)


You could clean up your main body by creating game_mode_1 and game_mode_2 outside of main and calling them for your if and elif and then just reduce your last elif to an else statement:

def game_mode_1():
    words = ['letters', 'sloppy', 'bedroom', 'jazzy', 'discovery', 'wistful', 'unadvised', 'help', 'line', 'shake', 'mend', 'time', 'attempt', 'dare', 'straw', 'destroy', 'health', 'shiny']
    theWord = random.choice(words)
    clear()
    game()
    break

def game_mode_2():
    theWord = str(input('Please write here the word: '))
    clear()
    game()
    break


You would then have: 

#using game_mode in place of gameMode, snake_cases again
def main():
    welcome()
    while true:
        try:
            game_mode = int(input('INPUT: '))
        except ValueError:
            print('Write 1 or 2 please.')
            continue

        if game_mode == 1:
            game_mode_1()

        elif game_mode == 2:
            game_mode_2()

        else:
            print("Write 1 or 2 please.")


Furthermore you could reduce main by creating user_selection

def user_selection():
    while true:
        try:
            game_mode = int(input('INPUT: '))
        except ValueError:
            print('Write 1 or 2 please.')
            continue

        if game_mode == 1:
            game_mode_1()

        elif game_mode == 2:
            game_mode_2()

        else:
            print("Write 1 or 2 please.")


And then your main would look like this

def main():
    welcome()
    user_selection()


Then run main adding if __name__ == '__main__': guard, this will prevent main from running if you import this script into another script

if __name__ == '__main__':
    main()