How can I reinstall Play Store? I was having some issues with my samsung galaxy s2. I took it to an I.T. store to get it fixed and now all is working fine, except play store is no longer there. I went into 'all applications' in settings and  play store is not there either so there is no way for me to set it back up. When I try and download straight from the internet version of plays store, an error tells me I do not have a device. Can anyone please tell me what I can do to fix this or if there is any other way for me download apps such as facebook and snapchat? Thank you in advance.
Of course you can install all your applications via their .apk package, downloadable from the internet (you'll also find several alternative markets like aptoide and F-Droid).
As of play store: the website only tells the android app to install a certain app, so if you don't have it installed, you won't go any further. 


install play store via it's .apk  there
if, once it is installed, it opens and then closes immediately, it is possible that the company that fixed it flashed a firmware without it. In this case, you'll need to flash the appropriate GApps package


PS: I highly recommend to flash gapps as most apps have google-modules dependencies (for instance google play services)