Other users make posts?

Go to Users tab. Click the checkbox beside the user(s) for which you want to change roles. Click the [Change role to …] drop down. Pick the role you want for user(s). Click the [Change] button.

Edit: Be VERY wary of giving anyone other than yourself the Administrator role.

OK, this is a help. But how about people who come to my site for the first time and want to post something?

I may be mistaken, I never made that, but that makes sense for me :

Give them the wp-login adress (must be yourblog.com/wp-login), there is a “create account” link.

In your admin options, allow users to create an account, and set the default user role to a role that allows the creation and publication of a blog note.

And there you are ??

But how about people who come to my site for the first time and want to post something?

No sane blog owner wants to allow that…
Eventually, you can let people you know to write a draft for approval by an admin or an editor – but completely leaving open a blog for anybody to publish, that’s not a good idea.

It is even better if you try to use this plugin: no need to register or login, just a form for submitting a post/article.
https://www.ads-software.com/extend/plugins/tdo-mini-forms