hello. i am new to this platform. How do we program into arduino without using any library to blink an led.
By using direct port writes. (digitalWrite() is part of a lib)
If you are new to Arduino, I suggest that you learn to blink an LED WITH the libraries first.
Then, once you get this working, replace the library calls (one at a time) with code that does not require the library. Remember that there is initialization of the Arduino prior to the first call to setup(). You will eventually need to remove or replace this as well.
The library source code is available to you for study. Study it!
Well you probably can avoid using the Arduino libraries. However, given the nature of the AVR processors, I strongly suspect you will need at least the compiler libraries to do various calculations.