photoshop eraser tool not showing on menu tool bar

All Tools are in the Toolbar usually on the left side unless you removed it.

Go to the Window menu and see that "Tools" at the bottom is checked on.

You should see the Toolbar as shown on the left: I've clicked on the Eraser Tool to make it active. It's usually  there by default.

You should also see the Context sensitive Tool Options Bar at the top. Again, check it on under Window > Options if you don't see it.

If you still don't see the Eraser Tool, go to Edit > Toolbar to get to the "Customize Toolbar" dialog and click on "Restore Defaults" and "Done".

Goto menu Window and mark the entry Tools.