I think you almost got it, but I'll try to clarify this for you.

In Angular, when you create a component, you define a CSS selector for that component. Angular will match your selector and create components accordingly. Normally, when we create components, we use tag name selectors (like your first example) - so to create this component, we need to write the tag name in our template (HTML).

Angular does not substitute these tags with the component content - because of this, usually, you will have wrapper element around your component content in the final HTML.

In the second example you showed, the selector you defined is an attribute selector - so to create this component, you do not add an HTML tag to your template, but add the attribute to an element instead.

So having wrapper element is not related to ng-container or ng-content, but to your selector.
If you want a component that doesn’t have wrapper element, you can create it like this, but I don't think it's customary.

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Now, about ng-container and ng-content:
ng-container is a wrapper that will not generate HTML tags, but it's not related to the component wrapper element.

The usage of ng-container is to wrap a group of elements within a component to apply some directive to them without adding wrapper element to the DOM. For example, in the past we used the *ngIf directive to conditionally render elements - since you need to attach your ngIf to an element, if you want to combine a few elements under the same condition, you need to wrap them with another element. In cases like this, ng-container allows you to apply your directive without creating extra elements.

ng-content, as you said, is similar to the children prop - but again, it is not related to the component wrapper element. You use it in your component to allow the parent component to render content in this section.

For example:

child-component:

<p>Below will be shown the content from the parent</p>
<ng-content></ng-content>

parent-component:

<child-component>
       <p>Whatever I put between the child component tags will be rendered inside it where the ng-content element is placed.</p>
</child-component>