1. Indicates a supposition and result: "If...then."
NOTE: This usage is similar to -ba although -tara sounds somewhat more gentle. Tara is likely to be used when the result is an intention, request (command), or question.
Sono ryōri ga amari tsurakattara, watashi wa tabenai wa.
If that dish is too hot, I won't eat it.
Kare ni attara, yoroshiku to itte kudasai.
If you see him, give him my regards (say hello).
Yamada-san no tsugō ga warukattara, dare ni wāpuro o tanomimashou ka.
If Yamada is busy who shall we ask to do the word processing?
2. Used at the end of a sentence to indicate a proposal; used often by women: "how about, why not."
Mō osoi kara, sono shigoto ashita ni nasattara.
It's late, so why not do that work tomorrow?
Sore wa chīsaikara, kochira no ōkī no o okai ni nattara.
That one is small, so why not buy this big one [instead]?
3. Used at the end of a sentence to indicate irritation or impatience, with a meaning something like: "I tell you, I'm telling you."
NOTE: Whereas with the above usages -tara is added to a verb stem in the same way as past-tense ending -ta, in this usage -ttara is added to the -te and -nasai form of verbs.
C'mon, get a move on.
Go to bed, I say [I'm telling you]!
4. Indicates an action which is followed by something being learned: "when."
NOTE: To is similar to -tara in this usage.
Tomodachi no ie e ittara, kare wa rusu datta.
When I went to my friend's house, [I found that] he was out.
[I went to my friend's home, but he was out.]
Hoteru ni denwa o shitara, heya wa ippai datta.
When I called the hotel, [I found that] all the rooms were full.
[I called the hotel, but all the rooms were taken.]
5. Indicates that one action follows immediately upon another: "when, as soon as."
Watashi ga koe o kaketara kite kudasai.
Please come [right away] when I call you.
Kono shigoto ga owattara, sochira e ikimasu.
I'll be there as soon as this work is done [as soon as I am finished here].
Hope this helps!
°˖ ✧◝(○ ヮ ○)◜✧˖ °こゆうきあいはら°˖ ✧◝(○ ヮ ○)◜✧˖ °