Choose the USB stick and press <span class="keycap">Enter</span>. The USB stick appears as an external hard disk and might be labeled <span class="guilabel">EFI Boot</span> or <span class="guilabel">Windows</span> like in the following screenshot:
[[!img install/inc/screenshots/mac_startup_usb.png link="no" alt="Screen with the logo of an internal hard disk labeled 'Macintosh HD' and an external hard disk labelled 'Windows' (selected)"]]
The <b>Troubleshooting Mode</b> entry disables some features of the Linux kernel and might work better on some computers. You can try this option if you think you are experiencing hardware compatibility errors while starting Tails.
The <b>External Hard Disk</b> entry makes it possible to [[start from an external hard disk|doc/advanced_topics/external_hard_disk]] and some [[problematic USB sticks|support/known_issues#problematic-usb-stick]].