Welcome to Android Central! For any modern device with a lithium battery, there's no absolute need to charge it to 100% -- you can start using it right out of the box, since most devices come with the battery around 50-60% charged. Lithium batteries aren't like older NiMH batteries, where charging fully was important.
That being said, when you first get a phone, you're probably going to be using it intensively the first day, with system updates, app installations, and other personal configurations, so you'll likely use a lot of battery. Therefore, it's generally a good idea to charge up to or near 100% to prepare for that.