Google Play is probably the biggest app store by the total number of available apps. Its advantage is, that there are many applications available on one website. But you can download apps for a mobile phone or tablet also from other app stores, websites for software downloading or company websites of software creators.
It is recommended to download apps only from trusted websites.
You can get apps for mobile devices also on webs focused on software download like: Uptodown.comSoftonic.com