how do we know which version mod is being used?

do the mods that we download and install auto update themselves when someone released a new update to it or do we have to do that manually?

and is there any way to know which version mod we are using for whatever addon thatis preinstalled to what is available in the marketplace?

example...here https://www.opencart.com/index.php?rout ... rch=square

it says it was updated nov 15th but i dont see a version number, and when i go into the payment modules i dont see a version number there either. how do i know if i should download that mod and update the one on the store?

There's no such thing as autoupdate in OpenCart. And version information solely depends on particular developer. Sometimes there's even none.

Don't rely on the "update" date for version numbers. That date is changed whenever anything on the extension page changes, including the tags or description, so it's not a good indicator of an actual extension update.

Usually version numbers for extensions are in the download files, or in the files themselves (often at the very top) so double-check that. Like thekrotek says, though, sometimes there might be no version information at all, if the developer didn't include it.

There are few important points you must remember:

1. When an extension is updated on opencart.com, it could be due to change in text, change in price, change in images and so on. It is not necessary that the extension's code was changed.
2. Doing versioning of the extension is purely a prerogative of the developer. Opencart or any CMS for that matter does not have any strict policy for that.
3. There is no auto update of extensions available on opencart.com . I heard they are providing this in the next version of opencart, which is progressing on a snail's pace.