Im not being able to select any vertices, edges or faces

That is weird, if they become highlighted that means they are selected. So if you are box selecting them and they highlight in orange or whatever color you have assigned to your UI theme, they are getting selected and then you can do any transform or operation to them. Can you post a screenshot of the problem, or better yet, a video screen grab of the thing in action.

You mean you can't left click and drag to box select?

Do you have any 3rd party add-ons enabled?

Or maybe Sana RRoxie ,

You have the wrong Selection Mode enabled, like Subtract, for instance:

Thanks for sharing the video Sana. It may be what Martin says. Also I see in the outliner you have the reference image selected. Make sure you only selected the mesh and then go into edit mode.

I see that you don't have your Tool Settings enabled in the Header:

Can you give us more context please? I don't know exactly what you mean by command key. Are you rotating? When your performing what operation are you trying an angle? The A key is for selecting all or deselecting.

Hi Sana,

the Knife Tool takes some getting used to.

Maybe practice on the Default Cube a bit until you get the hang of it.

Press K, then Enter and then you can press A to constrain to an Angle (increments of 30° by default). Pressing A more than once cycles through different options (Screen/Relative/Off/Screen...)Screen is the one you probably want here.

Watch the options at the bottom of the 3D Viewport:

That's an older Blender Version then 😊...it used to be C ...they changed that to A in 3.0