first of all, not every 737NG has these features installed.
But as the name indicates the speed and altitude intv. buttons intervene with FMC programming. (speed and altitude constraints)
Use the ALT INTV. during climb or descent to delete altitude restrictions in the FMC between your current altitude and the selected MCP altitude.
The SPD INTV works (as the alt. intv) only in VNAV mode.
Pushing that button will display target speed in the speed window, you can now change FMC target speed by rotating the speed knob.
And finally; No you can't push the altitude selector as in the Airbus. Instead of pushing the alt knob, Boeing has a VNAV button instead
