A lot of WordPress plugins are available in the market to show your Facebook page in the widget area. But a very few are there to show a button linked to your Facebook page. So, there is way you can add Facebook buttons to your websites manually.
Head to https://developers.facebook.com/docs/plugins/
You can add any button plugins but for now I am showing the process with the like button. The process will be same for any other button you want to add.
Click on like button from the left menu.
Go to the area like button generator.
Input your Facebook page URL.
Click on get code.
Now just copy the codes that has been generated,
And paste it to the widget area or page area and the button will be working fine. If they don’t work, make sure you have copied both the areas of the code properly. If problem persist check here , where I have discussed in detail about social plugins.