Cha-Am is right on Highway 4 about 200 km south of Bangkok, 30 km north of HuaHin, and 40 km south of the town of Phetchaburi.
From BKK you may take a taxi (1500 Baht, 2.5 hours). Many hotels in Cha-Am will offer to pick you up at the airport (1500 Baht, 2.5 hours).
The el cheapo alternative is to take a taxi from the airport to the Southern Bus Station
(sai tai mai in Thai) and get on the air conditioned VIP bus. (taxi 150 Baht, 20 minutes, bus 120 Baht 2.5 hours).
From HuaHin and Phetchaburi you may take the cheap and frequent local yokel orange bus for about 15 Baht.
Buses in Thailand are color-coded. The more orange it is the more local it is and the more blue it is
the more express it is. So when taking long inter-city buses make sure they are ALL blue with NO orange.
Cha-Am is nestled against the Gulf of Thailand and is graced by a long stretch of curved white sand beaches. It is adjacent to a fishing village. The local delicacies are squid (plamuek) and a small fish called platoo. Along Narathip Road are a string of chicken bbq places that produce a unique product known the world over as Cha-am style chicken.
If you are driving, take highway 35 south and west from Bangkok thru Samut Sakhon and Samut Songkhram until highway 35 dead ends at highway 4. At highway 4, turn left (south) and go thru Phetchaburi and follow the signs to Cha-am. It's easier than it sounds. Figure about 100 miles and 2 to 3 hours depending on traffic and where in Bangkok you started.