UNOS and ALGUNOS are two indefinite words, which meaning is not always easily distinguished. Let’s see how to use them:
1. The two words are interchangeable in the phrase algunos/unos when used with otros (otros):
Algunos/Unos vinieron, otros no (Some came, others didn’t).
Algunos/Unos dĂas estoy de nervioso, otros no (Some days I am nervous, others I am not).
2. Only algunos is possible in the phrase algunos de:
Salimos a cenar con algunos de mis amigos (We went out to dinner with some of my friends).
ComprĂ© algunos de los libros que me habĂan pedido (I bought some of the books which I had been asked).
3. Only unos/unas can be used to make non-generic nouns act and adjectives. Compare:
Son payasos (they are clowns –by professions).
Son unos payasos (they act like clowns).
4. Only unos/unas can be used in plural reciprocal constructions:
En el funeral se saludaron los unos a los otros (At the funeral they greet one another).
5.  Algunos is used when no implication of “a few” is intended, but uncertainty about who they are:
Algunos estudiantes hablan bastante bien español (Some students –we don’t know who of them– speak Spanish quite well).
But when “a few” is intended the two are interchangeable again.
 Me dio algunas/unas monedas (He gave me a few coins).
What do you think? It is not difficult, we just need to pay some attention, why don’t write some sentences with UNOS and ALGUNOS and leave them in the comments, we will be happy to correct them for you!