Search Engine Forums, SEO Forum

It's an off-page activity in SEO and people do guest posting more nowadays compared to article submission.

Article Submission is a off page optimization and it's help for Improving the keyword Ranking
This is one of the content marketing strategy

It's an activity in SEO (Off-Page)
in which people write and publish their article on third party website to get backlinks in return.

Typically article submission has various aspects. For example, the article we write on other websites must match their existing content tone, useful for their readers, and also describe our brand/product/ service(whatever you are writing for). We will have one or more backlinks in the content. Search engine loves this kind of backlink.
Sometimes, we have to write for their readers only do not adding our own refs anywhere in the article. We generally get backlinks in our profile area. Though it does not have much value if you are consistently writing the content then, you will build a good profile and the search engines will think, you are a genius writer. Not writing for backlinks etc.

Another aspect is, that you want to drive traffic from that website, make brand awareness, and increase social media followers.

In the end, focus on the quality of the website and match with your industry, if you post an article on a car selling website and get backlinks for your furniture products website. Then you will end up having a spam link. or the search engines will not consider it or do not pass any link juice to your website, hence ranking will remain the same.

Though your page and da rank will increase.