If it rains later, we'll (will) stay at home.
In the second part of the sentence you can use "going to" or the "Imperative" as well as "Will".
|Ex: turn off the TV when you go to bed|
|Ex: Change the channel if you want|
"If" can be substiutted by the following words:
"Unless + positive verb" can be used instead of "If……not" You'll be late unless you go now = You'll be late if you don't go now
When Turn off the TV when you go to bed
As soon as is more immediate than when. I will go to the toilet as soon as the commercials start.
In case: use for something you do as a precaution. Ex: Take your umbrella in case it rains.
Until (or till): up to the time when. Ex: we'll stay here until the dinner is ready
Use the first condional for Likely or possible situations.