If you mean you have two workbooks atht you would like to have as one, then open
both, then pick one and select all sheets by clicking on the first tab, holding
down SHIFT and then clicking on the last tab. Now right click, select Move or
Copy, then from the dialog box presented choose your other file from the
dropdown (Do NOT tick the create copy option, else you may end up creating
unwanted links between the files) and hit OK.