How to print in A4 sheet in excel because sometimes I'm not able to print in A4?

First thing before you print from excel you should set the print area and then you can choose the paper type and print it

Select the Cells you need to print then Page Layout > Print Area > Set print area.

Now check Page break view whether the print are you set will fit into one sheet or you need to print to multiple pages.

Now Set A4 as your paper size and print.