It’s common knowledge and instinctive to click on a different sheet tab in a workbook to activate it. You can also use the keyboard; press Ctrl-Page Up and Ctrl-Page Down to go up and down the sheets.
If your workbook contains a large number of sheets they may not all fit on the screen and it can then become tedious to scroll through the tabs or use the keyboard to get to a distant sheet.
You can though display a list of sheet names by right-clicking one of the arrows to the left of the sheet tabs at the bottom of the worksheet window (see below). Simply select a sheet from the list and you go straight there.