Can somebody tell me what would happen if I put the groud and neutral in the same bar in the subpanel?

This will be confusing and difficult to understand by novices.

The neutral conductor, while grounded and cannot measure voltage, is a current carrying conductor. Using a volt meter will show zero volts +/-, but using an amp meter will show the current being used by that load served by that circuit.

A neutral/ground connection has the serious potential of sending current out on the grounding conductor to the exposed metal frames of devices and appliances and will be a shock hazard.

Loose connections in wiring and more likely appliances will cause arcing and be a fire hazard.

Will increase the impedance of the grounding conductor, and in the event of a short circuit may not allow the short circuit current to flow properly and trip a circuit breaker in time to prevent a fire.

Don't do it.

Very often you do not have a choice, given the length of wire, or access to the neutral and ground bar. In the main panel, the neutral and grounds are not isolated, and putting them in the same bar or not isn't a real issue. But in a sub-panel, the neutral and the grounding bars (buss) are not connected. The neutral is isolated from ground and the ground is bonded to the panel. Look in most any main panel and you will see both the ground and the neutral sharing the same buss.

Thank you very much.