I just went through this the other day, first, hope that the person you buy it from knows how to pack things. The seller of mine did not, cue much worrying from me (even though I know PayPal would have covered me) when a crushed box arrived on my doorstep.
Take pictures as you remove it all from the packaging, that way you cover yourself in case anything arrives damaged. Remove and inspect the props, remove the gimbal cover and power everything on. Calibrate the controller, compass, IMU etc and go through all the settings with the props removed. I had some issues updating firmware and calibrating the sensors, but was able to perform those tasks using the desktop program.
Once you are happy everything looks good. Put the props back on, give them a wiggle to make sure they are attached. Set it to beginner mode and go fly.
My first flight I kept it fairly low and close to me, just getting a feel for the controls. Not looking at my tablet screen, but watching the drone. That was yesterday afternoon, drained 2 batteries and called it a day. I had also watched a handful of videos on beginner settings, what to expect with the drone, definitely worth spending the time doing that, I found them very useful.
Went back out today, switched off beginner mode. Again, spent some time just flying around watching the drone itself. Took it up to 200' and took some pictures, flew all around the yard, drained batteries again then the wind picked up. I cannot wait to get back out with it, it's really an impressive little thing. If you have Android, I've found an app called UAV forecast handy, I set the wind speed to 15mph and it's been nice to use to get an idea of winds.
Be safe and have fun with it. Sorry for the long post, but as I wrote above, I just went through all of this.