If you pitch in it means to join in enthusiastically in order to assist or help with an activity or work. To pitch in can also mean to contribute an opinion or give ideas during a conversation or meeting. This is a phrasal verb used in both social and professional contexts.

1. It's very easy to live with Ben. He's always happy to pitch in when there's housework to be done.
2. If everyone in the community pitched in we could eradicate all the litter on our street in one weekend.

1. I know you're new here, but don't be afraid of pitching in during meetings. I always like to hear fresh ideas.
2. The teacher was very moved when she found out that her entire class had pitched in to get her a going away present.