When should I use "una"?
When should I use "una"?
Sometimes it is just the word like "sandías" and sometimes it is like "una fresa"
2 Answers
Here's something to get you started 
Spanish Articles are used... with abstract nouns La pobreza es un grave problema. Poverty is a serious problem.
with titles of people El señor López abrió la conferencia. Mister López opened the conference.
with infinitives used as nouns El practicar deporte es bueno para la salud. Practising sports is good for your health.
with nouns listed in a series Tengo el libro, el cuaderno y el diccionario. I have the book, notebook and dictionary.
with a noun of weight or measure Las naranjas cuestan tres Euros el kilo. The oranges cost three Euros per kilo.
with days of the week El curso de español empieza el lunes. The Spanish course starts on Monday.
when telling the time Son las doce. It is twelve o'clock.
with parts of the body or clothes Voy a lavarme las manos. I'm going to wash my hands.
to generalize Los españoles se acuestan tarde. Spanish people go to bed late.
you should say uno when you have uno when your playing uno the card game
