Most Spanish verbs have a reflexive/pronominal form. In most cases this form does not change the meaning of the verb, for example:
Meter - meterse = to get (something) in - to get oneself in.
Creer - creerse = to believe - to believe of oneself.
In other cases the meaning does change:
Hallar - hallarse = to find - to be located.
No hallo mis lentes = I do not find my glasses.
¿Dónde se halla el banco? = where is the bank located?
The "reflexive" ending in the infinitive form is "se". But this form is often placed before the verb and conjugated accordingly to every pronoun.
Casarse = to get married.
Yo me caso
Tú te casas
Usted se casa
Él se casa
Nosotros nos casamos
Ustedes se casan
Vosotros os casais
Ellos se casan
However if the verb is not conjugated, the particle "se", is left at the end of the verb.
Ella no quiere casarse = she does not want to get married.
In impersonal constructions, it is best translated into English as "to be"... but this is NOT because "se" MEANS "to be"... it does not... this is just the way it should be translated into English.
Luego de la pintura, SE colocan los libros allí.
After the painting, the books ARE placed there.
¿Cómo SE supone ella que haga eso?
How IS she supposed to do that?
SE robaron mi teléfono.
My phone WAS stolen.
Your sentence "nos molesta" means "it bothers us", "molestamos" means "we bother".
I hope this helps.