This was copied from Grammar page 4 to get things started. Please edit and expand.
There are several different ways of adding the 'if' meaning to a sentence. Here えば, たら and なら are covered.
- えば Replace the final 'u' of the romaji version with 'eba'. For example the godan verb 'aruku' becomes 'arukeba'. The ichidan verb 'taberu' becomes 'tabereba'.
歩けば十分かかります。arukeba juppun kakarimasu.
If you walk it will take 10 minutes.
- たら is formed the same way as the past tense of the dictionary verb with ら added. So 'iu' goes to past tense 'itta' to 'ittara'.
手伝うと言ったらそうするでしょう。tetsudau to ittara sou suru deshou.
If he said he'd help then he will.
- なら goes after the dictionary form of a verb.
手伝う（の）ならさっそくはじめてください。tetsudau (no) nara sassoku hajimete kudasai.
If you're going to help, get started now please.
Example usage (～ represents the main sentence):
S1 と S2 (verb) 行く → 行くと～ (i-adj) 暑い → 暑いと～ (na-adj) きれい → きれいだと～ (noun) 私 → 私だと～
と is a subordinate conjunction which makes S1 a condition, and S2 a result. The nuance that is implied by usage of と is this: if the condition of S1 is satisfied, then the result of S2 follows naturally (and will always be true provided S1 holds true).
運動すると、体が良くなりますよ。 If you work out, you will become healthier. 日本は夏になると、ものすごく暑くなるよ。 In Japan, whenever summer comes along, it becomes way too hot!
Since と represents a natural consequence, it cannot be used when the result S2 is dependent on volitional action of someone. For example, S2 cannot be something like a command, invitation, or suggestion. Here is an example of incorrect usage of と:
If you're hungry, let's go to a restaurant. おなかが空いてると、レストランに行こう。 (incorrect) おなかが空いているなら、レストランに行こう。( correct)
もし is a word that goes at the start of a sentence and lets you know that an 'if' phrase is coming up. もし can be added to all of the above example sentences.
Special 'if' phrases
Some useful phrases ...
If it is ok with you... [let's do this...]
If you want (it), - when offering something to someone