Hi Farah @biijeeyjeey ,
With the Bevel Modifier not working, the problem is often, that Clamp Overlap is enabled (it is by default):

But if the Tool also isn’t working, it might be, that you haven’t Applied the Scale of your model.
– In Object Mode, CTRL+A > Apply > Scale.
To be honest, there could be quite a few other things be going on, but I’d need some more information then (screenshots can often be helpful).