ALPHA MEGA328 use ATMEGA328P-AU as it's microcontroller，which is same to Arduino UNO.You can use ALPHA MEGA328 the same way as Arduino Uno.

1. same bootloader as Arduino UNO。
2. operating voltage can be switched betwween 3v3 and 5v。
3. build-in 3v3 low dropout regulator， stable 3v3 power supply。

ATMEGA328P-datasheet
schemetic