Download through app store: Most Android phones have built-in App Store, where you can search for and download X. For example, you can search for X in Google Play Store, pea pods and App Store, and choose the appropriate version to download.
Download via browser: You can search for official website of X in the mobile phone browser, and choose the appropriate version to download after entering official website. Pay attention to choose official website with regular channels to avoid downloading viruses or malware.