// Get session

info := new(mgo.DialInfo)
info.Username = "username"
info.Password = "password"
info.Source = "admin"
info.Addrs = []string{"host"}
info.Database = "dbname"

session, err := mgo.DialWithInfo(info)
if err != nil {
    fmt.Printf("dial fail %v\n", err)
    os.Exit(1)
}
defer session.Close()

// Error check on every access
session.SetSafe(&mgo.Safe{})

// Get collection
collection := session.DB("dbname").C("collectionName")

// Delete record
err = collection.Remove(bson.M{})
if err != nil {
    fmt.Printf("remove fail %v\n", err)
    os.Exit(1)
}