There is no positive or negative in AC. Connect the yellow one with the green stripe to ground. If there's no distinctive marking on the other wires, you can connect either one to the current-carrying branch circuit wires. The difference in the black and white house wires is that the white is the grounded conductor (i.e., the neutral). Some fixtures have exposed metal parts that are connected to other than ground and you want these connected to the neutral. In fixtures that actually have an explicit ground wire, usually, it doesn't make a difference.

The usual effect of putting a dimmer on a "non-dimmable" fixture is that the light won't dim at other than full on, it either flickers or just goes completely out.

thank you for your comment! so as long as i keep it as full on, it wont affect the light fixtures? like fire hazard..stuff like that

What kind of bulbs does your fixture have? If they are regularly sized screw base, then you can replace them with dimmable LEDs. No harm in experimenting!