The most easy way is to attach the TrueType font in an email then send it to yourself and open the attachment on your iPad or iPhone.
You can also use the “Install your TrueType fonts” option in the app menu. (See attached screenshot 1)
On your computer, copy your TrueType fonts (.ttf or .ttc extension files) into a iCloud Drive folder then on your iPad, tap the "Install your TrueType fonts" and browse to those files and tap on them (Screenshot 2).
Once installed, your fonts will appear on the font list (screenshot 3) and they will be ready to be used on your texts.