Open the Settings app
Tap Display & Brightness
Adjust Text Size using the slider
Turn on Bold Text if desired
Open Settings
Tap Accessibility
Tap Display & Text Size
Adjust Larger Text if needed
Use a font app from the App Store if you want a different font style
Install the app and follow its instructions
Use the font in supported apps only
Change the font inside apps that offer font settings, such as Notes, Pages, or Word