Vue3

Global Register

import { createApp } from 'vue'
import App from './App.vue'
import DropdownMenu from 'v-dropdown-menu'
import 'v-dropdown-menu/css'

const app = createApp(App)

app.use(DropdownMenu)
app.mount('#app')

Local Register

<script setup>
import DropdownMenu from 'v-dropdown-menu'
import 'v-dropdown-menu/css'
</script>

Via CDN

<script src="https://unpkg.com/vue@3"></script>
<script src="https://unpkg.com/v-dropdown-menu"></script>
<link rel="stylesheet" href="https://unpkg.com/v-dropdown-menu/dist/vue3/v-dropdown-menu.css">

<script>
  const app = Vue.createApp({})
    
  app.use(DropdownMenu)
  app.mount('#app')
</script>