i have problem when i use Serial Monitor , all i can see is Symbols i cant understand a thing
i have win 10 by the way
Have you checked that the serial speed in your sketch matches your serial monitor?
You don't give us much to go on.
Garbage on the serial monitor typically indicates baud rate mismatch between what the serial monitor is running at and what the sketch is running at.
It can also happen if your're compiling for a different speed than your board is running at (this is not normally an issue with Arduino, since the upload would fail since the upload baud rate of 8mhz boards and 16mhz ones is different - but if you're uploading via ISP instead of serial, you don't have that sanity check). If you're running a standalone arduino running on the internal oscillator, you should not expect serial to work under all conditions - the factory calibration of the internal oscillator is not accurate enough for serial. Of course, these are all just different ways to get a baud rate mismatch. If you're running some weird setup where the serial monitor is connected to software serial, and you try to print to serial while receiving, both sides will get garbage; software serial is half duplex, you can't send and receive at the same time, and it doesn't deal gracefully if you try.