This is my first Atmega project so I have following questions:

1. Do I have to connect all those gnds and vcc's?
2. In programming I used Vcc Reset Gnd Tx Rx SClk of USART0 is that okay?
3. I didn't used external clock generator (quarks) because I'm planning to use inside clock?
4. Is there any fundamental circuits or pins that must be connected to work simple code? (I connected only Vccs and Gnds)
5. Is there simple circuit that tests if the atmega 128 is working or not without programming it?
['https://electronics.stackexchange.com/questions/206967', 'https://electronics.stackexchange.com', 'https://electronics.stackexchange.com/users/89445/']
1. **Yes.**
2. Only if you've programmed it with a serial bootloader already. Otherwise use ISP or HVPP as normal.
3. Okay? This is not a question.
4. AVCC must be connected. You probably also want to connect nPEN to a switch.
5. No. They come unprogrammed from the factory other than the ATmega103 compatibility fuse. Don't forget to unprogram that fuse before use.
@1: Yes, you have to connect all VCC and GND pins. This includes AVCC and AGND.

@2: Does the device run your program? Did the programmer return any error code?

@4: Connect a decoupling capacitor for every single VCC pin. Rule of thumb 100nF ceramic.

@5: Some devices may support JTAG testing or similar debug interface (debugWIRE), but I doubt that qualifies for "simple".