Most verbs in Spanish have a reflexive, also called "pronominal" form.
For example:
Poner - ponerse (to put - to put on oneself)
Tomar - tomarse (to take - to take / to take oneself)
When these conjugate with a pronoun, they use the object pronouns.
yo pongo - yo me pongo
tú pones - tú te pones
él pone - él se pone.
And so on.
Formerly, these pronouns could be placed either before the verb, like in the examples above or after them:
Yo me llamo = yo llámome
Tú te llamas = tú llámaste
Él se llama = él llámase.
Today are only a few of the verbs that are really used in this way. Most verbs will naturally be used with the object pronoun before them.
Sometimes both forms will have the same meaning and will only differentiate in its use.
Ir - irse (to go)
Tengo que ir.
Tengo que irme.
Both mean "I have to go". Both can be used in almost any circumstances, though, the first one will be used by a journalist on camera, it is very unlikely that he would use the second... on camera, though, he may use it with his boss. It is not impolite, or disrespectful, it is just lest solemn.
In other occasions they will have a different meaning.
Hallar - hallarse (to find, to be located)
Ellos hallaron una casa = they found a house.
La casa se halla en medio del bosque = the house is located (literally "finds itself") in the woods.
In the case of the verb olvidar, it has a pronominal form, that is "olvidarse". In both forms, the verb means the same:
No te olvides de cancelar
No olvides cancelar. (if the reflexive form is not used, then the preposition "de" is no necessary).
Mean exactly the same.
I hope this helps you.