Combining breast milk

Katie • 20 years old, FTM to baby boy Kaden Chance 💞👶🏻☺️
It says you can combine your breast milk you pump through out the day together.
What I was wondering is how? 
 Do I refrigerate the milk then the next time I pump add it to the already refrigerated milk, etc? 
 Or do I keep the milk out and add to it each time I pump that same day?  
Also, what if I want to freeze this milk? How does that process go?
Thank you! FTM