拉到一边

One day,he took me aside and promised me a sliver fourpenny on the first of every month if I would keep my eye open for a sailor with one leg and let him know the moment he appeared.

有一天他把我拉到一边，向我保证每月初给我四便士，如果我能留心注意一个只有一条腿的水手，且在他（水手）出现的那一刻告诉他。