Iba caminando hacia el puesto
Un joven que pasaba por mi lado tenía la inmortal obra en la mano y me la mostró. Luego me señaló un puesto de libros que estaba en la acera..Quería decirme que ahí podía conseguir el libro. Iba caminando hacia el puesto cuando oí que alguien me llamaba.
Question 1.....I don´t know why it´s iba caminando. iba is pretérito imperfecto of Ir. But I don´t know why we need Ir here in this sentence, ir caminando? I think if it´s not pretérito imperfecto, if we put it into present tense, would be , voy a caminar, right? But why it´s ir + caminando?
Question 2.... Can I only say Iba caminando hacia el puesto cuado oí que me llamaba. . without alguien is ok or not??
7 Answers
There are a few of these verbs of motion (ir, seguir, andar, salir, entrar, continuar, venir etc.) that are used with the gerund to add a special connotation.
Ir + gerund: Sometimes, ir is used in the same way as andar, above. But it usually doesn't have the negative connotation. In fact, it usually suggests that the action in progress is proceeding gradually or steadily. Again, translations of ir followed by the Spanish gerund can vary with the context.
- Vamos estudiando mejor la situación real del pueblo. We are coming to study better the real situation of the people.
- Fueron comprando trozo a trozo el terreno durante un proceso de unos quince años más o menos. They went about buying the land one piece at a time during a process that lasted 15 years more or less.
- Los estudiantes van ganando influencia. The students are steadily gaining influence.
Iba caminando hacia el puesto cuando oí que alguien me llamaba.
I was walking towards the stand when I heard somebody was calling me.
As Heidita said:
You can also say "...when somebody called me."
Hope it helps to organize your mind.
Iba caminando hacia el puesto cuando oí que alguien me llamaba.
You could have said:
...cuando me llamaban/llamaron.
Kiwi - Am I missing something? Sure it would flow better if you said, - he told me that I could get the book there. I started walking towards ...
but I think you can get away with - I was walking towards .... as 'iba caminando' expresses. It does put a bit of a pause between the two thoughts (being told and then walking) but that isn't too important is it? It just gives you the feeling that there's a small break between the two things happening.
That's actually what I meant (but it's pretty late 
), and I edited my post to reflect that idea. In my eyes though, it's more desirable to aim for writing without such "jars," shall we say, unless they're necessary to prove a point or serve some symbolic purpose because, at least for me, when I get jarred like that and a transition is a little rough, I get lost and think I missed something and have to go back and reread.
Consider the following:
I like to read. Reading is fun. I like playing video games. They're fun. They make me feel good.
as opposed to:
I like to read because it's fun. For the same reason, I like playing video games, which also make me feel good.
It reads a lot better, doesn't it? (At least, in my sleep-deprived state, I think it does. 
) Neither one is more correct than the other, but the first one jumps from ideas and you could start to get lost if there was a lot of material written like that. The second one is easier to read, and you can tell when the idea is changing as you read and not have to pick up on it all by yourself. Personally, I'd prefer to read something written like the second one so that I wouldn't get lost in all the jumps.
So, yes, you could get away with "caminaba hacia..."—I'd think it'd need to start a new paragraph too—but I think that, for the sake of the reader, "iba caminando hacia..." is the better choice of the two. 
Question 1: I believe that "iba caminando" in this case is used to mean "I went walking" or "I started walking." It also wouldn't make as much sense to say "caminaba hacia el puesto" because the text would have given no indication of the start of him walking. It would be rather jarring in English to see:
He told me that I could get the book there. I was walking toward the stand when I heard someone call me.
There's no transition to the walking. "Caminé hacia..." wouldn't make sense either given the following part of the sentence.
I walked toward the stand when I heard that someone was calling me.
There's no sense of the ongoing action of the walking here when he heard the call (as opposed to "I was walking/I went walking").
Question 2: Taking out "alguien" makes the sentence mean either that the boy from earlier called him or that the narrator called himself. I suppose you could get away with "se me llamaba" (I was called [by...] ). "Alguien" in this case serves as the subject of the verb "llamar," and the meaning of the sentence changes when the subject changes.
I hope that helps! 
Ir caminando often means to go on foot
Iba caminando is the past equivalent of the present progressive so it fits with the other tenses in your text - I am walking/going on foot ? I was walking/going on foot
Freeze - It would be rather jarring in English to see:
He told me that I could get the book there. I was walking toward the stand when I heard someone call me.
Am I missing something? Sure it would flow better if you said, - he told me that I could get the book there. I started walking towards ...
but I think you can get away with - I was walking towards .... as 'iba caminando' expresses. It does put a bit of a pause between the two thoughts (being told and then walking) but that isn't too important is it? It just gives you the feeling that there's a small break between the two things happening.
