Ramp Agent reported the tow bar was inadvertently not connected during pushback resulting in an aircraft breakaway before another ramper was able to chock the nose and pilots re-set the brakes.

Narrative

2 days out of training. Before departure; I made sure to follow standard procedure of removing the ground power; putting bypass pin and hooking up tow bar. When I moved the tow bar up to the landing gear; I remembered to put the bypass pin in before the tow bar so I put the bypass pin in first but then forgot to hook up the tow bar so when it was time to remove the chocks and release the brakes; I noticed that the plane was moving backwards without the tow bar being attached to the nose landing gear. I did not remember what to say to the pilot when it happened because I panicked and yelled out to my lead. I did not remember or recall to tell the pilot 'break away'. My lead then quickly chocked the nose landing gear as it was moving so when he did; it turned left. The pilot then asked why the plane moved backwards. I told the pilot that the tow bar was not hooked up and to re-set the brakes. After that; the ramp supervisor was called along with the maintenance who then told the pilot that he could straighten the nose landing gear by turning it back to a straight position.