>>557
会う is meet
合う is to match, suit, go with, etc.
However, 合う is also used for compound verbs like 話し合う、付き合う、めぐり合う、愛し合う etc. In this context, it can be understood more as "meet or come together" but the meaning is still closer to a "match" or "mutuality".
えば - what follows is always of natural consequence, a request, a thought, etc.
時間があれば、会議を参加するつもりだ
If there's time I plan on attending the meeting.
もっと詳しく説明してくれば、ありがたいと思います。
I'd appreciate it if you could explain in more detail.
勉強さえしすれば、いい点を取れることになる。
You'll get a good score if you just study
~たら purest conditional, may or may not happen, if or when
帰ったら、亡くした腕時計を探してみる
When I get back home, I'm going to try looking for the wristwatch I lost
学生全員が卒業式に早速行ってくれたら、問題なく始めるようになる。
If all the students could come to the graduation ceremony without delay, we'll be able to begin without a hitch.
ドアを開けたら、雨が降っていたと気づいた。
When I opened the door, I noticed it had been raining.
と literary or fictional use, when this-then this, when this-what?, etc.
公園に入ると、見知らぬ男に殴られた
When I entered the park, I was struck by a man I had never seen before
雪が降ると、外でよく遊んだものだ。
I used to play outside often when it snowed.
なら probable the easiest: ONLY used for "if" "then" when you receive information, circumstances, opinions, etc. from OTHER people and create a thought BASED OFF of that information
そうと思うなら、はっきり言ってくれ
If you think so, just tell it to me straight
休暇を取れないなら、週末も働いてもらえないか？
If you're not able to take a vacation, can I get you to work this weekend to?