To download WhatsApp for desktop, you have two main options:
From the official WhatsApp website
Go to: https://www.whatsapp.com/download
Select your operating system (Windows or Mac).
Download and install the app.
From the Microsoft Store or Mac App Store
Windows: Open the Microsoft Store, search for WhatsApp, then click Get.
Mac: Open the Mac App Store, search for WhatsApp Desktop, then click Download.
Logging in
Open the WhatsApp desktop app after installing.
On your phone, open WhatsApp → tap the three dots (Android) or Settings (iPhone) → Linked Devices.
Tap Link a Device and scan the QR code shown on your desktop.