Hello to all the mommies,
This is a one stop solution for mommies who  are worried regarding there milk supply and baby weight gain.The Supplemental nursing system (SNS) consists of a container and a capillary tube leading from the container to the mother's nipple.
The SNS container can be filled with fresh pumped breastmilk, with fresh donor milk, with pasteurized donor milk, or, if no human milk is available, with infant formula.
The tubing is usually attached with removable tape. When the newborn infant suckles on the breast, the infant is nourished both by fluid from the capillary tube and by the mother's breastmilk from the nipple. The mother's milk supply is stimulated by the infant suckling, and in most cases the use of the SNS can be discontinued in a few days or weeks when the mother's milk supply has risen to meet the infant's needs.

You can get more clear idea by watching videos on YouTube search by writing SNS feeding system.