This is really simple and i am sure most people know how to do this but here it is step by step
first search for the app you want which will be an apk file download it to a computer or straight to your tablet, if you download it to a computer transfer it to your tablets sd card. then follow these steps

  1. First go into settings-applications and check unknown sources
  2. Use a file explorer app to find the apk file(most tablets have them pre installed).
  3. Open it, find the apk file and click install.

hope that helps some if you have any questions just ask
Here is a video on how to install a file browser if your tablet doesn’t have one, also shows a little of how to use it to side load apps
//www.youtube.com/embed/Yfw_U5nQlTg
sorry about the video quality I couldn’t find my good camera hope it still helps     

www.coastal-connection.com.remotesupport.aspx