Boot your 3DS while holding Select (if you use boot9strap) or launch the TWiLight app from your home screen.

Today, the process has been revolutionized by and nds-bootstrap running on modern flashcarts or modded 3DS consoles. The QR code method streamlines installation entirely.

In TWiLight Menu++, press Start to open the Settings menu. Scroll down to "Download Play" or "QR Code Downloader." The location varies by version; in v25.0+, it is under "Tools."