The Latin abbreviation et al. is short for et alia (et aliae, et alii), meaning and others (alia is masculine plural, aliae is feminine plural and alii neuter plural).
When referring to literature, the abbreviation is used to replace author or editor names when there are more than two (in some cases more than three) authors or editors:
Simon et al. (2000) showed the importance of R&D for production.
This has been pointed out in previous research (e.g., Eriksson et al., 2016; Palm et al., 2016; Platts et al., 1996).
Make sure you put the full stop in the right place! The word et is not abbreviated but alia is, so the full stop must be after al.
When you write et al., the verb must of course have its plural form:
Simon et al. (2000) have pointed out that …
In the possessive form, et al. is followed by an apostrophe and an s:
Simon et al.’s (2000) contribution to research …
Latin words are sometimes italicised in English text, but abbreviations should not be in italics, unless the publisher requires it.
You will find some common Latin abbreviations in English here.