¿With or without tilde?

You: Acute, grave o esdrújula?

Spanish teacher: and sobresdrújulas.

You: sobresdrújulas, too. Oh no, that is too much!

The rules of accentuation in Spanish allow us to know how and when we should use  the graphic accent. We will start with acute words.

Agudas words are those whose major stress is on the last syllable and we must add the graphic accent when these words end in N, S, or any vowel, but if they do not end in any of these letters, it is not necessary to write the graphic accent although the prosodic accent is maintained.

Example: Demolición (It ends in N and is acute).

                Allá (It ends in A (vowel) and is acute).

                Detrás (It ends in S and is acute).

                Comer.(The stress falls on the last syllable, but it does not end in N or S or vowel

                             therefore, it is not accented graphically).

Graves

Graves words are those whose major accentuation falls on the penultimate syllable, they will be accented graphically if they end in any letter that is neither N, nor S, nor vowel. If they end in any other letter, they must be accented graphically. 

Example: Débil. (It ends in L, therefore when grave, it is accented graphically).

                Lápiz. (It ends in Z, therefore when it is grave, it is accented graphically).

                Pila. (It ends in a vowel, but since it is grave, it should not be accented   

                         graphically).

 Note:      These words are also called llanas.

Esdrújulas

These are words whose major stress is on the antepenultimate syllable. These words are always stressed no matter what letter they end in.

Example: Pájaro.

                Párrafo.

                Esdrújula.

Sobresdrújulas

These words have the major force of voice in the syllable before the antepenultimate syllable and always carry the graphic accent. That is to say, they always have the accent mark, just like the esdrújulas.   

Example: Ajústatelos.

                Envíamelos.

                Empíricamente.

Summary

CasesTone SyllablePut the accent mark.Example
AgudasLastIf end in  N, S in vowel. Tapón
GravesPenultimateAny letter that is neither  N, nor  S nor Vocal.Frágil.
EsdrújulasAntepenultimateAlwaysPétalo.
SobresdrújulasBefore the antepenultimate.AlwaysPréstamelo. 

Give your own examples!