Download APK from the link above. It's a good experience to check the file for malware. So, use your antivirus program or try a free one – AVG AntiVirus Security. Once you get.apk file, click on it in Downloads and install on your Android device.
You can easily uninstall Steam. Go to Apps & Notifications, choose the app, tap it and select Uninstall. Keep in mind that some files can be lost while removing the app.