diff --git a/interfaces/13-io/main.go b/interfaces/13-io/main.go
index 1cf2cd8..3f753c8 100644
--- a/interfaces/13-io/main.go
+++ b/interfaces/13-io/main.go
@@ -49,6 +49,8 @@ func main() {
 	}
 }
 
+// ioCopy streams from a file to another file.
+// we use it to stream from the standard input to ouput.
 func ioCopy(dst, src *os.File) error {
 	// Use a fixed-length buffer to efficiently read from src stream in chunks.
 	buf := make([]byte, 32768)
@@ -76,6 +78,7 @@ func ioCopy(dst, src *os.File) error {
 	return nil
 }
 
+// write method example.
 func write(dst *os.File, buf []byte) error {
 	nw, ew := dst.Write(buf)