There are several hundred functions on Excel, which can mostly be combined to produce thousands more, but sometimes even they cannot cope with requirements.

Excel’s programming language, VBA (Visual Basic for Applications) is there to help you achieve the missing capabilities, by allowing you to program Excel. Routines can be written, dialogue boxes displayed, and data manipulated.
You can even write your own Excel functions.

A very popular use is to automate oft-repeated operations, which are generally called macros, introduced by Lotus in the 1980s.

These can be written, but the most straightforward and popular method is have Excel record them for you.