In some way agreeable to his tender years, as in singing, or playing upon instruments of music, as they used then to do in God's service; or lighting the lamps, or some other way. For I suppose Samuel was not brought to the tabernacle in such tender years as some think; of which See Poole on "1 Samuel 1:22". Before Eli the priest, i.e. under the inspection and by the direction and instruction of Eli.
Related Commentaries of 1 Samuel 2:11
1 Samuel 2:11
11 And Elkanah went to Ramah to his house. And the child did minister unto the LORD before Eli the priest.