The most likely case is someone or a firm e-mail or DM you. This guide is about how to add Guest author in WordPress and of course, there are other viable option as well where you accept contents from others who are willing to do it for a backlink, sponsored post
There should be some kind of agreement or understanding between both parties. It can help you with traffic and improving your ranking but not the only factors you should consider
FIRST, Login to your dashboard and click on plugins option
SECOND, It will expand with a few option and click on the add new
THIRD, Type in Guest author in the rectangular box next to the keyword. Install and activate it.
FOURTH, Click on the Settings option when it expands choose the Guest author option from the list
FIFTH, Go to your posts and add a new post
I’ll skip the part about adding contents which I am sure everyone knows it by now
LASTLY, Scroll down the page which is on the right side of your interface under Document
Choose Guest > Add author name > URL > Description > Image.
The only thing left to do now is to publish the post/article