Open the Play Store. It will likely ask you to sign in. Note: You may need an "App Password" if you have 2-Factor Authentication enabled on your Google account, as the old login screen doesn't support modern OAuth well.
: You can still browse and download apps that have not yet raised their minimum API requirements above level 19 (KitKat). Basic Synchronization
What specific (if any) are you seeing when you try to open the store?
Sideloading a compatible bypasses these roadblocks, restoring full access to millions of apps that still support API level 19 (Android 4.4).
While installing the correct legacy APK will restore the interface of the Google Play Store, users must maintain realistic expectations. Because Google has officially ended support for the KitKat ecosystem, the vast majority of modern apps (such as WhatsApp, YouTube, Netflix, and modern banking apps) will no longer be visible or downloadable. Their developers have shifted minimum requirements to newer Android versions.
Fortunately, you can still easily enjoy apps on your KitKat device using alternative Android marketplaces that fully support older operating systems:
Search for or 17.3.16 . These versions are widely documented as the final stable releases that reliably authenticate with Google accounts on Android KitKat without immediate crashing. Step-by-Step Installation Guide