Trying to learn about SPI...

Okay, I've got a 7 segment led running from a shift register using spi... It counts from 0 to 9 and starts over

Now I want to add a button to count up or down...

Can I add an analog button to the arduino on another pin or do I have to put the button on the SPI bus?

No you don't.

The button to give you some sort of input to the program is nothing to do with the SPI driving the display.

Thank you.. Tim