nara v tara なら たら

from japanesepod.com
 Today's grammar point is -tara and -nara, both of which form conditional phrases. Tara is a subordinate conjunction. In English, this roughly corresponds to "when," "if" and "after." Nara is the hypothetical form of the da copula, which expresses the speaker's supposition about the truth of a present or past fact or the actualization of something in the future.　In English, this roughly corresponds to "if it is true that" or "if that's the case."

Formation: 
Tara: Verb / Adj (informal past tense) + ra

走ったら 
Hashitta ra

かわいかったら 
kawaikatta ra

Noun + datta +ra

雨だったら　
ame datta ra

Nara: Verb /i-Adj (informal form) + nara

勉強するなら　
benkyō suru nara

高いなら　 
takai nara

na-Adjective (stem) + nara

きれいなら　
kirei nara

Noun + nara

子どもなら
kodomo nara

Examples:

タクシーに乗ったら間に合うよ。　 
Takushī ni nottara maniau yo. 
If you get a taxi, you can make it.

明日、雨だったら、運動会は中止です。　 
Ame datta ra, undōkai wa chūshi desu. 
If it is rainy tomorrow, we won't do the athletic festival.

そんなに高いなら、買わないよ。　 
Sonna ni takai nara, kawanai yo. 
If it's so expensive, I won't buy it.

先生ならきっとおこるだろう。　 
Sensei nara kitto okoru darō. 
I bet my teacher would get angry.

着いたら、改札の前で待っています。 
Tsuita ra, kaisatsu no mae de matte imasu. 
When I arrive, I'll wait for you in front of the electronic ticket gate.