accessing the serial buffer on arduino uno

Can the serial buffer be accessed through any digital pins on the Arduino uno, or is it only accessed via the UART(pins 0 and 1)? For example, this article says the following:

Get the number of bytes (characters) available for reading from the serial port. This is data that’s already arrived and stored in the serial receive buffer (which holds 64 bytes). available() inherits from the Stream utility class.

You can't "access" the serial buffer through any pins. Pins 0 and 1 are connected to the USART that receives and transmits data. But the data has already passed through the USART by the time it is stored in the input buffer.

The usual way to get data from the input buffer is

Have a look at Serial Input Basics

If you explain what you want to do we may be able to give a more useful answer.