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ながら (nagara) is equivalent to "while" in English.

It is a connecting particle that is added to the stem word of a verb to connect phrases and clauses.

お茶を飲みながら話しました。(ocha wo nominagara hanashimashita.)
"we talked while drinking/having tea."

The last phrase sets the tense of the sentence.

If you want to say you are doing [main action] while doing [secondary action], you use -nagara.

Like, for example: While I sang, (main action) I played the guitar (secondary action). [Okay I get confused over which is the main action or secondary action in English, but you get my point, right?]

That would translate to: gitaa wo hikinagara utaimashita.

Sing = utau (utaimasu)
Play (string instruments) = hiku (hikimasu)

Singing is the main action while the guitar playing is secondary, therefore attach the -nagara to the secondary action.

To attach -nagara is easy. All you do is take a verb, let's say yomu (to read). Turn it into the polite form, which is yomimasu. Delete the -masu part and you will be left with the base stem yomi, in which all you do is add -nagara.

Ex. shinbun wo yominagara terebi wo mimashita.

While I was watching TV, I read the newspaper.

**NOTE** The subject has to be the same. You cannot say "I sang while my friend played the guitar" with -nagara. It has to be ONE subject only doing the action.