“We're trying to save up so that we can afford a house.”
You go out to a restaurant with your friend and don't want to order much because you're saving money. You say this to explain that you're saving because you want to buy a house.
We're trying to save up so that we can afford a house.
You may have heard that there's a difference between "try to (do something)" and "try (doing something)". In general, you should talk about a goal after "try to ___":
Try to get there by 10:00.
I try to make everyone feel comfortable when I host a party.
And talk about a method to reach a goal with "try ___ing":
I can never sleep on an airplane. I've tried listening to relaxing music, taking sleeping pills, staying up the night before. Nothing seems to work.
This means to save money and build it for a certain purpose, like buying a house or car.
You usually say "save up for ___":
I'm saving up for a new drum set.
Or you can save up "so that" you can do something:
We're saving up so that we can afford a trip to New York later this year.
The structure "___ so that ___" explains your reasons for doing something.
I'm trying to be quiet so that the baby doesn't wake up.
In normal spoken English, you can drop "that":
I'm trying to be quiet so the baby doesn't wake up.
This means to have enough money to buy something:
We can't afford to send our kids to private school.