diff --git a/README.md b/README.md
index 1d5d099..bf3cd71 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,47 @@
 # jhol
 
-Go language library to check Japanese holidays using Google Calendar.
+Go language library to check Japanese holidays using [Google Calendar](https://calendar.google.com/calendar/embed?src=ja.japanese%23holiday%40group.v.calendar.google.com).
+
+## Preparation
+
+1. Enable the API.
+    * https://developers.google.com/calendar/api/quickstart/go#enable_the_api
+1. Create an API Key.
+    * https://cloud.google.com/docs/authentication/api-keys#create
+
+## Usage
+
+```go
+package main
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/winebarrel/jhol"
+)
+
+func parseDate(s string) time.Time {
+	d, _ := time.ParseInLocation("2006-01-02", s, time.Local)
+	return d
+}
+
+func main() {
+	apiKey := os.Getenv("GOOGLE_API_KEY")
+	client := jhol.NewClient(apiKey).WithoutContext()
+
+	date := parseDate("2023-07-17")
+	h, _ := client.Get(date)
+	fmt.Println(h) //=> 2023-07-17	海の日
+
+	yes, _ := client.IsHoliday(date)
+	fmt.Println(yes) //=> true
+
+	holidays, _ := client.NextN(date, 3)
+	fmt.Println(holidays) //=> [2023-07-17	海の日 2023-08-11	山の日 2023-09-18	敬老の日]
+
+	holidays, _ = client.Between(date, parseDate("2023-08-11"))
+	fmt.Println(holidays) //=> [2023-07-17	海の日 2023-08-11	山の日]
+}
+```