Go to Settings > Display &Brightness .
It allows to adjust the brightness of your iPhone. Keep it low to save battery.
Night Shift : This Apple feature makes your iPhone screen warmer thereby making it less stressful for your eyes when used in the dark or during the night. Schedule it for auto on off or use it manually when needed.
Bold Text and Text Size :Allows you to change the text of your iPhone to suit your style.
View: This helps you to select the size of everything on your iPhone. Either Zoomed i.e big or Standard i.e Normal.