Meaning: This means that in a team, everyone is responsible for helping each other and working together to achieve a common goal.
Choice of Words: The word "one" means a single person or thing. "All" means every single person or thing. "For" means in support of or on behalf of. When you put them together, the sentence means that each person in a team is responsible for supporting and helping the other members of the team, and that the team as a whole is responsible for supporting and helping each individual member.