Functional Building are the building that you built at your bases Not used for warfare or battling purposes But used for Technical uses Like Generating rescources, Storing Rescources, Or just used as a plain Decoration.
Town Hall are the primary object that you must defend at any kind of conditions So many people always say "Don't forget To Put Town Hall In the Center Of Your Village" Upgarding Town Hall Is Used to unlock more and new feature of this game. But read this attention That player that attack you or attacked by you Has same level of town hall with you So Don't be surprised if level 40 player with same level of town hall attacked you that still in Level 20. Town hall also serve additional capacity of 1.000 elixir and gold. Destroying enemy town hall also give 1 star for your Raid.
Resources Generating Building
Gold mine are used to generating Gold resources that mostly used to build Elixir related object and Defensive Building . For more info click Title
Gold mine are used to generating Gold resources that mostly used to Warfare Based Building And To Train Units . For more info click Title
Gold And Elixir Storage
Both of this storages are used to Store your resources
Decoration Object is used to decorat your base to make it more beautiful than before but also serve as a partial Part Of your bases