Hydrogen, oxygen and nitrogen are counted as some most important elements and found abundantly. About 75% of this universe is composed of hydrogen and helps different other matters to sustain. Large starts and planets, electrons and protons are also composed of hydrogen.
A sheet tab appears at the bottom of your worksheet. It has the name of the worksheet on it, which can be changed and you can also change its colour. This can be done by right clicking on it and picking the option from the shortcut menu that appears. By clicking a sheet tab, you can make that sheet the active sheet so that you can work on it.
Microsoft like to argue that their Office suite is better supported than Google Drive and free equivalents but I'm not convinced by that. With Excel you can customise the ribbon (or toolbar for older versions) but the Google Sheets menu structure and toolbar is what it is. There's a larger range of formulae in Excel (but as I understand it both applications let you write your own functions that you can use as formulae).