Press "o" on the keyboard to toggle "on axis" on and off. Moving objects will be constrained to their x or y axis depending on movement.
Press "n" to toggle snap to guidelines on and off.
Press "g" to toggle snap to grid on and off.
These 3 will appear as icons at the left of the status bar at the bottom.
Also, when moving objects with the snap to guidelines and/or grid enabled, if you press and hold shift before moving the object(s) using one of the 9 squares in and around the selected object(s) you will snap to the exact point of selection. Bit hard to explain this in words, your best bet is to try this out, it will then make sense.
Regards,
George Z.