Obb files are additional data files for Android games. These are very beneficial if your device is not rooted. For example, if you smartphone's internal memory is 512 MB and if you want to install a game of 1 GB, then you cannot install it without rooting your device. So in this case, obb file plays a very important role.
How to Play .obb Games
Now coming to your question, you cannot open obb file directly. You need to have both the obb and apk file of the game. This apk file is just a shortcut/launcher/emulator of the obb file. Therefor, its size will be smaller than the original obb.
1. Firstly, place the obb file in the Mcard/Android/obb/ folder.
2. Now install the apk file.
3. Then goto the Menu screen nd you will see the icon of the newly installed game. In your case, it will be - Leos Fortune.
4. Now open it and enjoy the game. It will automatically execute the obb file place in the inner folder.