Google has added Play Store support to five more Chromebooks which means there are five more groups of consumers who can enjoy Android apps on their Chrome OS laptops. That being said, only three of the Chromebooks have official access to the Play Store in the stable channel. These Chromebooks include the Samsung Chromebook 3, the HP Chromebook 13 G1, and the Lenovo Thinkpad 13 Chromebook. If you have any of these three laptops then following a Chrome OS update when you boot it up next you should see some notification that the Play Store is available for installation. You shouldn't have to do anything special other than install the app and go through setting it up.
As for the other two Chromebooks, which are the Acer Chromebook 11 C740 and the Dell Chromebook 11 7310, Android app support through the Play Store is available but it's not available in the stable channel just yet. It is however available in the beta channel, so if you don't mind wiping your laptop's local data then you can swap to the beta channel of Chrome OS pretty easily from the settings menu and once the laptop finishes its process and boots back up, you'll be in the beta channel and should then be able to install the Play Store app, which in turn will give you access to loads of Android apps.
With these five Chromebooks newly added to the list of supported machines, Google is continuing to grow the list of Chromebooks which will be able to use Android apps and eventually, all Chromebooks will have this capability. As it stands the list of Chrome OS machines which have the Play Store sits at 59 according to the Chromium Projects Page for Chrome OS systems that support Android apps. Not all are Chromebooks as a few here and there are Chrome OS desktop machines, but the majority of them are Chromebooks. Google is also working diligently to add more Chromebooks to the list, so even if the Chromebook you own isn't supported yet, there are still many that are planned to receive this support and it will just be a matter of time.