A "steward", Greek oikonomos (Strong's number G3623 οἰκονόμος), literally means "the manager of an estate or household." In a sense we are all stewards, managers, of the resoures God has put into our hands. Paul and his colleagues were entrusted with the establishment of the church by preaching the gospel and organizing and caring for congregations. This role had been delegated to them by the Lord. Therefore, they were Christ's "stewards" carrying out this work on his behalf. See 1 Corinthians 4:1,2; Galatians 4:2; Titus 1:7; 1 Peter 4:10.
I hope you have found this helpful.