A full stop is used:

• to indicate the end of a sentence. Put 1 space after a full stop, not 2. The old typewriting convention of putting 2 spaces after a full stop has been dropped. Two spaces can actually detract from, rather than improve, readability and can cause problems with formatting

• to separate elements of the username (before the @) and domain name (after the @) of an email address

• to separate elements of the domain name of a URL

• as a decimal point

• to separate hours from minutes in times of day (a colon can be used as an alternative)

• to separate a filename extension from a filename in a computer file

readme.txt     document.docx

• to indicate ring size in chemical names.

Full stops are not recommended:

• at the end of headings
• after a person’s initials (see References).

Also use minimal full stops in abbreviations and contractions (see Acronyms and initialisms).

But follow the style of your organisation or journal, as appropriate.