Before you start learning past progressives, it is necessary that you understand how gerunds and present progressive tenses work, as well as the imperfect indicative tense. Since you have already had some experience with gerunds, you should know that you can use them with the verbs estar, seguir, andar, ir, and other verbs of motion to express that and action is either in progress or is continuing at the time indicated.
Sigo hablando. → I am still talking.
Ella está chismeando. → She is gossiping.
As you should already know, the imperfect tense can have a different meanings. It all depends on the context.
yo hablaba → I was talking, I used to talk, I talked
ella cantaba → She was singing, She used to sing, She sang
Past progressive with the imperfect tense adds a little bit of clarity.
yo estaba hablando → I was talking
ella estaba cantando → She was singing
You can also use past progressive with preterit
me fui gritando → I left screaming
ellos continuaron estudiando → they continued studying