I'm presuming the scanner works properly outside of Acrobat and is connected and ready to go.
From the File menu, go to the Create button in the toolbar. Click on "Create PDF from Scanner" then on the flyout menu,select "Configure Presets..."
Your scanner should be selectable from the Scanner drop-down list at the top of the dialog box. Click OK to confirm. TW is Twain, WIA is Windows Acquisition. I do not know exactly what you have,so see what works from the scanner selection menu.