different glRotatef use

Will this rotate about the y-axis by 60 degrees
and 30 degrees around the x-axis?

is this equivalent to:

No and no.
It will rotate 60 degrees around the axis defined by the vector (0.5f, 1.0f, 0.0f).

[ www.trenki.net | vector_math (3d math library) | software renderer ]

I want to have my engine set 3 rotational values for each object.
So shouldn’t these rotations be performed in one step, ie around the global x,y,z axis?

Or would I have to call
and then work out what vector will represent the global y axis
and then call
glRotatef(roty,myCalculated axis vector)
and then calculate a vector which will represent the global x axis?

OpenGL will compose the rotation matrices you specify into a single one under the hood, so you shouldn’t have a problem as long as you don’t hit gimbal lock.