The installer skips the Installer Destination, and defaults to the drive currently running the OS. How can I install Sierra on another drive?

The macOS 10.12 installer is missing from the Apple documentation because it is currently broken when it comes to creating a bootable USB installer. Even so you need to run the .pkg installer so it extracts the actual installer app to the Applications folder.

Instead of using the broken macOS 10.12 Sierra installer download the macOS 10.13 High Sierra installer since a 2010 laptop can run macOS 10.13. Then create a bootable macOS USB installer using these instructions (includes links to download 10.13):

https://support.apple.com/en-us/HT201372

Edit: You should also be able to boot into Recovery Mode using Command + R to reinstall macOS. If the laptop had macOS 10.12.6+ installed at some point, then you can also use Internet Recovery Mode (Command + Option + R) to access the online macOS 10.13 High Sierra installer.

If you still want to use Sierra then download the InstallOS.dmg then open it to InstallOS.pkg.

Double-click on InstallOS.pkg and an installation window will open.

This does not install Sierra but will create Install macOS Sierra.app in your Applications folder.

If you are asked to select a destination disk for this make sure you select your macs internal drive.

HWTech is correct there is a problem with making a bootable USB installer with the Install macOS Sierra.app

where it returns an error Volumes/<USBname> is not a valid mount point. There is a workaround.

With Install macOS Sierra.app in your Applications folder open Terminal.

Paste in this command

sudo plutil -replace CFBundleShortVersionString -string "12.6.03" /Applications/Install\ macOS\ Sierra.app/Contents/Info.plist

press return

enter your password

press return

now paste in the createinstallmedia command for Sierra where MyVolume can be replaced with the name of your USB stick.

If your USB name has more than one word separated by spaces you would need to type it in as

/The\ USB\ Name

sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ macOS\ Sierra.app

press return

follow the prompts