What does Ma Joad mean when she says “Why, we’re the people – we go on?”

This is actually a motherly pep talk. Ma isn't about to quit, nor is she going to let enyone get her down...... for long. Ma knows what they've already been through, as well as the fact that it isn't going to get any easier anytime soon. None-the-less, she sees the light on the other side, and she knows that perseverance will take them where they need to go.