it'll

This is a contraction of "it will". People use it in casual spoken English. Don't use it in formal writing unless you're trying to quote someone who was speaking casually.

His landlord reassured him that it was only a temporary inconvenience. "It'll be ready by Monday," he said.

"It'll" is similar to "this'll" and "that'll". All of these contractions are less common and less formal than the usual contractions like "can't" and "isn't".

the fridge

English speakers usually call their refrigerator "the fridge". For example:

I have some beers in the fridge. You want one?

The word "refrigerator" sounds a bit formal. You say "refrigerator" when you're talking about it as a machine. For example, when you're calling a repairman:

Can someone come out and take a look at my refrigerator? It's not staying cool like it's supposed to.

(some food) will keep for (some time)

Food eventually "goes bad": it becomes rotten, stale, or rancid. It's not safe to eat after a certain period of time. You can talk about that time period by saying that the food "will keep for ___":

A jar of honey will keep for decades if it remains sealed.

It will keep in the freezer for a couple of months.