After you pump you definatly put the milk into the refrigerator so it stays good. Most babies are going to want the milk warm, so prior to giving the bottle you can put it in a bottle warmer. They do not recommend the microwave because you can get hot spots in the milk that can burn the baby. We didn't have a bottle warmer. We would put the bottle in some hot water for a minute and let it warm up being extra careful to shake it up and test it before so its not too hot. My daughter liked her bottles room temperature so a lot of time when we knew a feeding was coming we would take the milk out of the fridge 20 minutes prior so it started warming up on its own.
You can warm up breast milk from the fridge or freezer. They even have bottle liners that you can pump in to, and when you're ready to use it, drop it in the bottle. I recommend a bottle warmer, my sister had one and it always warmed the milk perfect, never too hot!