For typing special symbols with a mac, pc, or iPad keyboard, you can use the Alt-Key Symbols for PC or the Option-Key Symbols for Mac, or a long press on the iPad. A subset of keyboard maps are attached for your reference.

When CREATING Boom Cards, you can also use Google to search the web for a special symbol and then copy it from your browser and paste it into your Boom Learning content.

SPECIAL NOTE: For students who need to type special characters into a fill-in-the-blank answer, you can use an "onscreen" Boom Learning keyboard.

To activate the special keyboard, in the DETAILS Dialog in the Deck Editor studio... select the "subject" tab.

Then pick an "onscreen keyboard" to use. 

All of your fill-in-the-blank answers will display the special keyboard to help students type special characters.

This is what it looks like to the student when trying to type into a Fill-in-the-blank answer.