If you are just using single character commands you can use == For example
if (inBuffer == 'a') {
Note, especially, the use of single quotes for single characters.
For future reference the cstring "a" would be comprised of the characters 'a' and '\0'
And this
char inBuffer = "";
should just be
char inBuffer;
and then this
while (Serial.available())
should be
if (Serial.available())
because you just want to read a single character
You should not have the line
stepper1.run();
inside any IF statement. It should just be called directly from loop()
...R