Summarize this article in one sentence.
Your "Settings" app will be somewhere on your home screen. Scroll through your pages until you find it. Your "Settings" app may look slightly different depending on which version of Android you run, but for most phones it can be identified by the gear icon. Each version of Android may have a different name for this area. Look for the option that has the word "Storage" in it. You can identify the right option by the SD card icon. On this screen, you will see info on your total SD card space, your available free space, and an option to "Unmount SD Card" and "Format SD Card". If the "Format SD Card" option is grayed out, you will first have to unmount your SD card. Tap on "Unmount SD Card" in this case. Your Android device will begin to format your micro SD card, and erase all its contents. You may see several screens that ask you if you are sure that you wish to format your SD card. Doing so will erase all the content on the card. Follow the prompts to erase and format your card. Once you have formatted, your card will be formatted to FAT32 filesystem type. All your content will be cleared, and you will have a new card formatted to your Android phone. Note: If you are using Android 6.0 Marshmallow, you will have the option to treat your SD card as either internal storage or portable storage. If you choose to use it as portable storage your SD card will be treated like any other removable storage, allowing you to remove it and transfer files to your computer or another device. If you make it internal, it will be formatted and not be allowed to be read by your computer. Your SD card will be treated as your main storage system.

Summary:
Tap on "Settings" from the Home screen of your Android device. Tap on the option that reads "Storage" or "SD & Phone Storage". Select the option for "Erase SD card" or "Format SD card". Tap on the option to confirm you want to erase the contents of your SD card when prompted to by your Android.