Don’t let the math scare you. It looks difficult because it is unfamiliar to you. Once you’ve reduced a few sights the “lightbulb” will go off. There are numerous worksheets, calculators, apps and computer programs available to help you with “the math” .
Bubble sextants can be used on land, sea or air.
You need some type of horizon, whether it is natural or artificial to take a sight. Artificial horizons come in a variety of flavors. You can use a pan of oil [not mercury!]. Davis Instruments manufactures an artificial horizon which can be used with any type of sextant. Celestaire manufactures a Practice Bubble Horizon which can be used on most modern marine sextants and Cassens & Plath manufactures a Professional Bubble Horizon which can also be used on most modern marine sextants.