There are many stuff you need to know when it comes to deletion tags.
Proposing an article for deletion Edit
If you are a regular user, you must propose an article for deletion before you make it a candidate. Depending on how many admins decide that the page should be deleted, it will be marked as a candidate and you have 3 days to improve it before it goes into the recycle bin. You must make at thread about it on the deletion board and give reasons why.
Candidates for Deletion Edit
If you are a regular user, you can only make pages normal candidates and you must propose it first. You have 3 days to improve it before it goes into the trash can. Even if your a bureaucrat, you still have to propose an article before making it a regular candidate.
Speedy Candidates for Deletion Edit
Pages can be instantly marked for deletion by rollbacks, chat mods, thread mods, and Semi-Admins without proposal taking place. If you wish to make it a regular candidate, you still have to propose it. Speedy Candidates are called Speedy because you only have 1 day to improve compared to the original 3 for a regular candidate. You should only use this ability when the article has too much mistakes to be proposed.
Very Speedy Candidates for Deletion Edit
Pages can be instantly marked for deletion even faster. Semi-Admins and lower (excluding regular users) can also use this ability, but if it has more than too much mistakes, that's the only time it should be used. If you mark an article for Very Speedy Deletion, you only have 2 hours to improve it.
Extremely Speedy Candidates for Deletion Edit
Extremely Speedy Candidates for Deletion can only be marked by Admins. If there's almost 75% mistakes, then you should mark it as an Extremely Speedy Candidate. The page creator only has 1 hour to improve it before it's thrown out.
Undyingly Speedy Candidates for Deletion Edit
The quickest candidate for deletion for now is here. You must be a bureaucrat to mark a page for an undyingly speedy deletion. The author will only have 5 minutes to improve the page before it is deleted. Only use this if 99% is nothing but mistakes.
Deleting an article without proposing or using any of the candidates Edit
This ability can be used by Admins and Bureaucrats and is probably the highest level of deletion. Normally, deletion happens when you run out of time to improve your page once it's any kind of candidate after being proposed. If the page has almost 9000% mistakes, you can instantly delete it. For some reason, even though this is the highest level of deletion, the previous level of deletion can only be used by Bureaucrats.