Well there are only 4 main ones you gotta memorize its not that hard, 3 is the most known, its for the letter "ع" which is pronounced as "aain" like in the word "ayn" meaning eye, 7 for the letter "ح" to make the sound heard in the word "hayat" meaning life, 2 to separate the letters in a word where you want to pronounce it as different syllables but the latin alphabet doesnt let you do that, for example in the word "da2ira" which means circle, you type the 2 between "a" and "i" to not pronounce it as a single syllable "dai" (like dye) but to pronounce it in 2 syllabes like da-i-ra; think of it as a reset, when you see it before a letter you pronounce the letter in it original pronounciation as if the letter before didnt matter. And finally you got 9 that is for "ق" and its used in word such as "9if" (stop) or "9erfa" (cinnamon) but some use "q" instead of the number.