“Oh well, it'll come back to me in a few minutes.”
You read a work email earlier today about a new potential client. Now you're talking with a coworker and trying to tell her about the e-mail. She asks you the name of the client, but you can't remember what company it was. You try hard to remember for a minute or two, but you can't, so you say this.
Oh well, it'll come back to me in a few minutes.
When you try something and it doesn't work, you can say "Oh well". Saying "oh well" shows that you're not too upset about it not working. People often use this to show that they've given up and stopped trying. Here's an example of something to say after you've been looking for your missing iPod headphones for 5 minutes:
Since this phrase shows that you're not worried about something not working, you shouldn't use it if you fail at something important. People will think that you didn't care or you didn't try very hard to be successful.
Use this when you're making a strong prediction about something in the future:
It'll take about an hour and a half.
When you use "will", it's a kind of personal promise that something will happen, so you only use it if you're sure. You wouldn't use it to say what you think the weather is going to be like, or to predict who will win a baseball game.
In casual conversation, you can pronounce "it will" as "it'll". You can even write it this way in casual writing, like on Twitter or in the comments of a blog.
This phrase is used to describe something that you can't remember at one point, but the memory returns later:
A: I can't remember the name of it.
B: That's OK. Just let me know if it comes back to you.
This is used when you forget names, dates, or other information.