So shared GPU memory is the amount of ram memory that will be used in case dedicated video memory runs out, that means that if a game needs 2gb of vram to run and my gpu only has 1gb of vram, I can use the ram memory to compensate for the lack of video memory and I can play smoothly without affecting performance?
You can use system memory to compensate for the lack of VRAM yes, but you will not be able to play smoothly without it affecting performance. As your game will keep swapping assets between VRAM and system memory, as well as the fact that system memory has significantly less memory bandwidth.
God no, if it has to seriously dip into system RAM performance will be really badly affected. This shared RAM is nowhere near as fast as the dedicated RAM on even a relatively slow card.