Looking at your video you have an object parented to an object in another collection. Just keep in mind when you parent objects they aren’t removed from their collections. Objects can be assigned to multiple collections. The child object is always shown in the expanded view of the parent. Almost all parenting is done in the 3D Viewport you can either use object->parent menu. In object mode, right click->parent menu or ctrl+p/alt+p hotkeys. If you want to do parenting in outliner it can be done by holding shift while dragging the child object(s) and highlighting the parent object. If you want to unparent then just shift+drag and drop on a collection or move to the left side if you’re putting it into the same collection. Also you can use shift+Alt+drag if you want to remove parent but keep the offset. As for moving it around in collections you can just drag and drop in outliner or use M key in outliner or 3D viewport. Remember the active editor is the one that the mouse cursor is over.
