After the full stop at the end of a sentence, type one space. Not two.
One space looks right and feels right and is right.
In the olden days, when typewriters ruled, people were trained to type two spaces after a full stop. That looked right on a typewritten document, but it looks wrong on anything you write electronically.
Some people still type two spaces and advise colleagues to do the same. Don't let this obsolete habit persist.