Difficult situations require courage. Not everyone can wait quietly and see how things turn out. Someone has to step up and help. You can be the one. Yes, you can be the "good" one, if you become a volunteer to help the others when they need it.
When you step up, you volunteer to do something important. Others will depend on you to do a good job. This idiom is similar to “man up.” However, “man up” implies that you do not hide from responsibility, and “step up” means that you actively seek it.
Did you know that " step up" comes from baseball? OK! I'll tell you that it really does. It comes from baseball because throughout the game, each player must step up to the plate and take his turn at bat. But you can step up in almost any aspect of your life. If your mother is sick, you can step up and take care of her. If an army needs someone for a dangerous mission, a good soldier will step up.
(Taken from Daily English lessons at http://www.englisch-hilfen.de/en/english_lessons.htm)
You can listen to the dialogue and then, check the grammar point for the Future simple form.
What does "responsibility" mean?
( If you look up in your dictionary, you will find these entries,
re·spon·si·bil·i·ty
noun, plural re·spon·si·bil·i·ties.
5.
reliability or dependability, especially in meeting debts orpayments.