- for what is the stop button?
Not much.
- do the upload button compile the sketch first or only uploading?
It should compile the sketch first, but I think it only does so if you save the sketch first. To be safe, you should compile first.
- what makes auto format?
It cleans up the indentation of your code, so that, for example, statement inside a block are indented two spaces.
- how can i send a serial command from the ide to the board? (serial_read_basic)
Right now, you can't. You'll need to use another program like zterm (on the Mac) or HyperTerminal on Windows. This feature should be added to the IDE soon.
- when i download led_blink, it needs several seconds until the execution starts? why ? is this optimizing? the same after a reset and a power on in stand-alone.
The delay when the board resets gives the bootloader time to see if a program is being uploaded to the board. If not, it will launch the program that's already on the board. Using the same pause after uploading helped squeeze the bootloader into less space on the board.
- what means the white number in the footer of the ide?
I believe that's the number of the line that you're currently editing (that the cursor is on).
The serial port speed in the menu only controls the speed used by the serial monitor. It should match the speed passed to beginSerial() in the code of your sketch. The speed used to upload the program to the board is always 19200, regardless of the menu setting (but it can be editing in the preferences.txt file as described in the FAQ).