How do I create a new text file anywhere on my Mac

One option is to open the TextEdit app (use the search icon magnifying glass on the menu bar to find it), click "New Document" when it opens, type the text that you want to save, click the File menu > Save item, select an existing folder (top red arrow below) or create a new folder (lower red arrow) and enter a file name (Save as box at top). See screenshot below:

Taking the text file request literally, one must select TextEdit's Format menu to Make Plain Text instead of Rich Text (.rtf) as shown in FoxFifth's screen shot. Although the Finder Quick Look facility won't care and will display both equally well, some applications other than TextEdit may not be able to open a Rich Text file.

In addition to FoxFifth's excellent suggestions:

Another way to quickly open Text Edit is to click it's icon in the dock (generally along the bottom of a Mac desktop.

Thank you kindly for your thoughtful reply :-)