How do you set the text font to the custom font?

How do you set the text font to the custom font bc I was making an app that lets you have some fonts to add in the list and save it.. I already got the info.plist and it has the Fonts provided by application property in the plist.. I added the whole font file name in the Fonts provided by application section But the main question is How do you set the text font to the custom font?