The imperfect is used to talk about what you used to do or what you were like in the past and to talk about actions that continue for an unspecified amount of time.
Cuando yo era joven, le decía a mi prima, "Tu vas a engordar". When I was young, I used to say to my cousin "You are going to get fat".
The verb decir (to say, tell) is regular in the imperfect tense.
The imperfect tense endings are: ía íamos ías íais ía ían
Mi prima decía en la conferencia qué importante es sembrar árboles. - My cousin was saying at the conference how important it is to plant trees. Yo les decía a mis amigas el año pasado que iban a viajar. - I was telling my girlfriends last year that they were going to travel. Tú le decías a tu mamá lo mucho que la amabas. - You were telling your mom how you love her. Cuando tenías a Félix, el gatito, le decías que jugara. - When you used to have Felix, the kitten, you used to tell him to play. Nosotros siempre les decíamos a nuestros hijos que se portaran bien. - We used to tell our children to behave well. Ellos decían frecuentemente que hay que comer comida sana. - They used to say frequently that it is important to eat healthy food.