You didn't read what I previously wrote.
Gmail works very similar to windows file manager.
Think about your emails like they are files in windows. The Trash folder/label in Gmail is like the Recycle Bin in windows. When you delete an email message, the message is not in fact deleted, but moved to a special folder/label called Trash and kept there for 30 days, for safety, in case you accidentally delete something important that you do not want to delete. As long as you do not Empty your Trash folder, you will always have stored in it all the email messages deleted during the last 30 days. So, these deleted files still use your storage space until you Empty the Trash folder.
The tabs the article is talking about do not use storage space. They are just a mean to ease your work, that is, to have faster access to different special folders/labels.
When an email message comes in to your inbox, it is checked and filtered by the program (in this case, Gmail). Depending on its content, Gmail assigns it a label, like Updates, Promotions, Spam etc. For example, if you click on the Promotions label, you will see only messages that Gmail "thinks" are promotions. The storage space used is the same, no matter under what label the message is. In order to really delete a message and free up the space it uses you have to delete the message first, then go to the Trash folder and delete it again from there or just Empty the entire Trash files.
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