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Are you downloading the apk file?
Getjar is an alternative app store (like the Amazon app store) - and is legit, so should be safe to use. I think it is popular in Russia/ eastern europe. Not used it in ages though - prefer getting stuff through the Play store.
GetJar - Wikipedia, the free encyclopedia
An APK file is the programme. Once it is downlaoded on an android phone, it either installs automatically (though it should ask for a prompt) or you need to browse to it and click it to prompt it to install.