Those kind of verbs are known as reflexive verbs. You can learn more about them here. As the adjective indicates those are the verbs whose action reflects into the subject itself. Using your example, when you take a shower, you're cleaning your own body, you're cleaning yourself.
They are also known as pronominales because the presence of a pronoun before the verb. This denomination is the one recommended by the RAE, one of the main authorities regarding the Spanish language.
First of all, remember that we tend to omit the personal pronoun because that information is already include in the verb tense. We use to say "me ducho" instead of "yo me ducho".
In case of doubt about the use of the reflexive pronoun, you can look for the verb in the DRAE, you'll find there this special annotation to indicate that the verb is reflexive/pronominal: "U. t. c. prnl." (Utilizado también como pronominal) or just "prnl." (pronominal)
duchar
- tr. Dar una ducha (‖ proyección de agua). U. t. c. prnl.
On the other hand, "comer" is a tricky verb regarding this aspect because you can say
Me como una barra de pan todos los días
or
Como una barra de pan todos los días
If you check comer in the DRAE, while it can be pronominal in some cases, in yours "me" is not mandatory and it can be omitted, the verb is not reflexive there. Both sentences mean exactly the same.