Golang Pointer Understanding

I am learning go and i need to understand something. I am getting few errors. I have created a Product struct and attached a func with it. I also got a product lists as a slice. Actually I am following one example. I was just trying add different endpoints to it.

I have added question in comment in code. Please explain. I need to return the json single object as a response to user. Please guide me.

package data 

type Product struct {
    ID          int     `json:"id"`
    Name        string  `json:"name"`
    Description string  `json:"description"`
    Price       float32 `json:"price"`
    SKU         string  `json:"sku"`
    CreatedOn   string  `json:"-"`
    UpdatedOn   string  `json:"-"`
    DeletedOn   string  `json:"-"`
}

type Products []*Product


func (p *Products) ToJSON(w io.Writer) error {
    e := json.NewEncoder(w)
    return e.Encode(p)
}

func (p *Product) FromJSON(r io.Reader) error {
    d := json.NewDecoder(r)
    return d.Decode(p)
}

var ErrProductNotFound = fmt.Errorf("Product not found")


func GetProduct(id int) (*Product, error) {       // this is returning *Product & err. When I use this in GetProduct in handler func it is giving error
    for _, p := range productList {
        if p.ID == id {
            fmt.Println(p)
            return p, nil
        }
    }
    return nil, ErrProductNotFound
}

var productList = []*Product{    **// Why in example the teacher doing it like this.** []*Product{&Product{}, &Product{}} **what it the reason? Please explain.
    &Product{                             // this gives warning : redundant type from array, slice, or map composite literal. need to understand why**

        ID:          1,
        Name:        "Latte",
        Description: "chai",
        Price:       2.45,
        SKU:         "abc123",
        CreatedOn:   time.Now().UTC().String(),
        UpdatedOn:   time.Now().UTC().String(),
    },
    &Product{
        ID:          2,
        Name:        "Tea",
        Description: "chai",
        Price:       1.45,
        SKU:         "abc1234",
        CreatedOn:   time.Now().UTC().String(),
        UpdatedOn:   time.Now().UTC().String(),
    },
}
package handlers

func (p *Product) GetProduct(rw http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    id, _ := strconv.Atoi(vars["id"])
    p, errr := data.GetProduct(id)  **// cannot use data.GetProduct(id) (value of type *data.Product) as *Product value in assignment**
    errr = p.ToJSON(rw) // **p.ToJSON undefined (type *Product has no field or method ToJSON)**
    if errr != nil {
        http.Error(rw, "could not locate the product", http.StatusBadGateway)
    }
}