A conjunction is an invariable element that links other elements within the sentence. Coordinate conjunctions link two or more small sentences that could be used as independent sentences. Here are a few examples:

sin embargo - however
siquiera - even
de todos modos - anyway
pero - but
no obstante - nevertheless, in spite of
ni -neither

Let's look at some example sentences.

Yo di mi palabra y no voy a ser candidato.
I gave my word and I won't be a candidate.

Ni me dijo que se ha comprado un coche ni que le despidieron en el trabajo.
He didn't tell me he has bought a new car or that he was fired at work.

O está cansado o es demasiado difícil.
Either he is tired or it is too difficult.

Sea que no lo entiende, sea que no quiere entenderlo.
Wether he doesn't understands, whether he doesn't want to understand it.

Nosotros comimos helado aunque teníamos frío.
We ate icecream eventhough we were cold.

Eché gasolina al carro, sin embargo el motor no arranca.
I put gas in the car, nevertheless the engine won´t start.

María no habla sino que grita.
María doesn't talk, she rather screams.