The Spanish word for a/an is ‘un‘ for Spanish masculine nouns and una for Spanish feminine nouns.
Examples;

Todos deberian tener un pasaporte (masc’) = everyone should have a passport.
Por aquí hay sola una habitación libra = there is only one room vacant here.

Note, that Spanish does not use the equivalent of English ‘a’ when you indicate [...]

The use of ‘por’ and ‘para’, both meaning ‘for’ or ‘by’, can be a bit confusing at first.
The difference is that;

‘por’ looks back to the origins of, or the root causes of  the circumstances;
‘para’ looks forward to the result, aim or destination of the  the circumstances.

Spanish ‘Por’ is used to express, or used with;

Cause, reason, [...]

The Spanish prepositions — ‘a’ (to), and ‘de’ (of), when used in conjunction with a Spanish noun, precede the articles (el),(masc’) and (la) (fem’).
When these Spanish prepositions come before the masculine (el), ( singular), there is a contraction and fusion of these two.
Therefore; (a + el)  =  al, and (de + el)  =  del.
Single, masculine [...]

The Spanish preposition ‘desde’ can be used;

With time and duration, (tiempo y duración);
–viene en tren desde Zaragoza = he/she is coming from Zaragoza by train.
–Este quadro está desde1800 = this painting is from the 1800’s.

The Spanish preposition ‘con’ can be used ;

With company, (compania);
– me quedo en casa con todos los demas – I’m staying [...]