¡Era muy bonita! and En el jardín había una piscina muy grande

Question

Hola,I have a couple of questions on this activity:Question1:why the use of the imperfect here:  Kwizbot ¡Era muy bonita! Question 2: Kwizbot En el jardín había una piscina muy grande You En el jardín había una muy grande piscina How to learn this structure, what rules govern this use.  Thank you for your help,Nicole

Inma Sánchez · Accepted Answer

Hola Nicole
With reference to 1., we are using the imperfect "era" because we are simply "describing"; the speaker has no intention to focus on this being a completed action with an end (where you'd use the Indefinido - fue); It is just descriptive.  
Here is a lesson about this usage of the Imperfecto. 
With reference to 2., the natural order in Spanish is "noun+adjective", unless there is a specific purpose to change it and place the adjective in front. For this there is also a lesson -have a look here. 
Saludos
Inma