Sometimes the DM will call for a group test. Group tests take place when the entire party is engaged in a single task, such as climbing a cliff or sneaking up on an enemy camp. The more skilled members of the group are able to help the less skilled members.
In a group check, every player makes a d20 Test as described here. If more than half of the group succeeds in their d20 Test, the group as a whole succeeds. If half or less of the group succeed, the group as a whole fails.