Bangkok the Capital of Thailand is huge and it's the typical city you usually encounter in other country; however, Bangkok is divided into two areas: New and Old City.

The Old City consists of Grand Palace, China Town, and few other tourist attraction and next to the Chao-Phaya River. There is no BTS service in the Old City, you will much rely on taxi, tuk-tuk, and boat (if you travel on river) most of the time.

As for New City, it consists of  tall, big buildings, busy streets, traffic jams and so forth. It's quite similar to any Capital City you can find in other developed country.

If you intend to explore the culture heritage of Thailand, aim for the Old City.

Quick Tips:

At the Biyoke Sky Hotel you are able to watch and enjoy the night scenery of Bangkok at the top (88th floor).

The Grand Palace is a HUGE palace for King of Thailand last time. The palace is so huge that I had to use nearly half day to explore it.

Wat Pho is near the Grand Palace and it's a huge Buddha statue. 

Wat Arun is also near Grand Palace, but need to cross the river by using boat.

The Khaosan Road is a backpacker paradise, guesthouse, pub, restaurant, shopping....you name it , you have it.