You can download it for free.  Open the App Store. Make sure that you are connected to a network. Search for "Dropbox". Tap "Get" and then "Install" next to the Dropbox app in the search results. The app may take a few minutes to download and install. Dropbox accounts are free and come with 2 GB of storage. You can pay to increase your available storage. Tap "Sign Up" and follow the prompts to create your account. If you already have an account, you can tap "Sign In" to get started. When this is enabled, any new pictures and videos you take with your iPad will be automatically backed up to your Dropbox account. You can disable or enable this later if you change your mind. If you're just using the free account, you may want to disable this feature, as pictures and videos can quickly fill up your Dropbox.

How would you rephrase that briefly using Chinese?
从iPad设备上的APP Store（应用商店）中下载Dropbox应用程序。 打开Dropbox应用程序，创建新账户。 决定是否启用“从相机上传”功能。