Using nara なら
There are several ways to express the meaning behind 'if' in Japanese. なら is one of them. It is a conjunction that means 'if the preceding phrase is true, then...'
It may be best to memorize example sentences.
-i Adjectives: Adjective + なら [You can also use の: -i Adj + の + なら]
takai nara, kawanai.
If it is expensive, I won't buy it.
omoshiroi nara, mitai.
If it is interesting, I want to see it.
Verbs: Plain form + なら [You can also use の: Plain form + の + なら]
anata ga iku nara, watashi mo ikimasu.
If you are going, I'll go too.
chokore-to o taberu nara, ha o migakinasai.
If you are going to eat chocolate, brush your teeth.
okane ga aru nara, terebi o kainasai.
If you have money, go ahead and buy a TV.
Also here are a few common usages with nouns:
anata nara, dekiru.
If it is you (doing it), you can do it. (it can be done)
otona nara, sonna koto wa shinai.
An adult wouldn't do such a thing.
(if it is an adult, the adult wouldn't do such a thing.)