CONJUNCTIONS

Conjunctions connect various elements in a sentence.     They can be as simple as:   

Pedro y Carlos

 - Peter and Charles
libros y revistas - books and magazines

or a little bit more difficult such as:

Ni Juan ni su padre lo superion hasta ayer

 - Neither John nor his father found out until yesterday.
O me dices la verdad o vas a sentirlo. - Either you tell me the truth or you're going to regret it.

There are three types of conjunctions in Spanish: coordinate, subordinate and correlative.

Coordinate

Coordinate conjunctions connect words, phrases or clauses of the same kind.  The most common are:

o

 - or
ni - nor
y - and
pero - but
sino - but

peras y fresas

-

 pears and strawberrys

en la cocina o en el comedor

-

 in the kitchen or in the dining room

listo pero perezoso

-

 cleaver but lazy

NOTE

Both  "o"' and "u"  mean "or".  You normally would use "o" to mean "or".  However, when a word ends in "o" and the word that would follow "or" begins with an "o", or "ho" use "u".

muchachos u hombres - boys or men septiembre u octobre - september or october

The conjunction "o" when used with numbers becomes "ó".

2 ó 4 - two or four

Both "y" and "e"  mean "and".  You would normally use "y" to mean "and".  However, when a word that would follow "and" begins with "i" or "hi" use "e".

bonita e inteligente - pretty and intelligent madre e hijo - mother and daughter
aguja e hilo - needle and thread padre e hijo - father and son

However, when a word that follows "and" begins with "hie" use "y".

flores y hierba - flowers and grass nieve y hielo - snow and ice

Aquí se encuentran cobre y hierro.

 - Copper and iron are found here.

Fortunately there are not a lot of words in Spanish that begin "hie", but the list does include:
hielo - ice
hiena - hyena
hierro - iron
hierbabuena - mint

Pero usually follows an affirmative expresssion, but may follow a negative statement if the verb of the first clause is repeated or if another ver follows.

El es inteligente pero perezoso. - He is intelligent but lazy.
Bebe leche pero no bebe café. - He drinks milk but he does not drink coffee.
Juan no bebe café pero bebe leche. - John does not drink coffee, but he drinks milk.

Sino is used only after a negative in a contrasting statement when the verb of the first clause is understood but not repeated. 

Juan no bebe café sino leche. - Juan does not drink coffee, but milk.

Subordinate

Subordinating conjunctions join subordinate (dependent) clauses to main clauses.  A subordinate clause is a group of words containing a subject and verb that is dependent on a main clause.  Commonly used subordinate conjunctions are:

a condición de que - on the condition that de suerte que - so that, in such a manner as
a fin de que - so that, in order that desde que - since
a menos que - unless después (de) que - after
a pesar de que - in spite of donde - where
antes (de) que - before e - and
así .... como - both .... and empero - yet, however, notwithstanding
aun cuando - even if en caso (de) que - in case
aun - even, still en cuanto - as soon as
aunque - although, even though hasta que - until
caso que - in case that luego que - as soon as, after
como - as, since mas - but
como que - it seems that, apparently mas que - even if, however much
como quiera que - although, since mientras - while
como si - as if mientras que - while, so long as, as long as
con la condición que - on condition that ni - neither, nor
con tal (de) que - provided that ni siquiera - not even
cuando - when para que - so that, in order that
dado caso que - supposing that porque - because
dado que - supposing that puesto que - since
de condición que - so as to que - that
de manera que - so that si - if, whether
de modo que - so that, in such a way that sin que - without

This above list English to Spanish
Less Common Conjunctions
ni sólo ... (sino) también not only ... but also ya que - since, seeing that
para que - in order that, so that en razón de que - for the reason that
pero - but entrentano que - meanwhile, while
por cuanto - inasmuch as más bien que - rather than
pues que - since no bien ... cuando - no sooner ... than
sin embargo - nevertheless por más que - no matter how
sino - but, rather por rázon que - for the reason that
sino que - but that, but rather that salvo que - unless
siquiera - though, although siempre que - whenever, provided that
tan pronto como - as soon as tan luego como - therefore
u - or tanto ... como - as much .... as

NOTE

In Spanish only a conjunction or a relative pronoun can introduce a subordinate clause.  As such you must be careful to use a conjunction in Spanish, although in English the word may function as an adverb, preposition and a conjunction.   A conjunction must be used when a subject and verb follow the main clause.

    Adverb   Preposition   Conjunction
English before before before
Spanish antes antes de antes (de) que
 
Incorrect Ellos llegaron antes saliésemos.
Correct Ellos llegaron antes que saliésemos.
  They arrived before we left.
 
Incorrect Suele salir sin nosotros lo oigamos.
Correct Suele salir sin que nosotros lo oigamos
  He usually leaves without our hearing him.
 
Incorrect Nos réimos después nos dio las buenas noticias.
Correct Nos réimos después que nos dio las buenas noticias.
  We laughed after he gave us the news.

Correlative

Correlative conjunctions are used in pairs with intervening words.

o ... o - either ... or apendas .... cuando - scarcely .... when
o sea .... o sea.... - either ... or

Apendas nos saludó, cuando tuvimos que salir.

-

 He'd scarely greeted us when we had to leave.

Ni Juan ni su padre lo supieron hasta ayer.

-

 Neither John nor his father found it out until yesterday.

O me dices la verdad o vas a sentirlo.

-

 Either you tell me the truth or you're going to regret it.