They all mean "about". The difference between them is when each is used.
"О" is used when the next word begins with a consonant. For example: о тебе, о маме
"Об" is used when the next word begins with a vowel. For example: об Америке
"Обо" is used when the word after it begins with the following groups of consonants: чт, вс, мн. For example: обо мне
Hope this helps! :)
"О Европе" is the correct one here. When at the start of a word or after another vowel, the letter "е" is pronounced "ye", with a consonant sound at the beginning. (This is also the case for the vowels "ё", "ю" and "я", which are pronounced "yo", "yu", "ya" when at the start of a word or after another vowel.) The word "Европа", although it starts with a vowel, is pronounced with a consonant sound at the beginning ("yevropa"), so you have to say "О Европе".
Russian has just one Present Tense so translating from English to Russian, both "are you reading" and "do you read" would be the same. However, when you want to translate it from Russian to English, it depends on the context. "Are you reading" is Present Continuous used for actions happening at the moment (Are you reading at the moment?) and "do you read" is Pesent Simple used for actions that repeat or happen usually (Do ypu read every day? Do you read often?)
о, об, обо take prepositional case. Мне is either dative or prepositional case.
Here's a list of prepositions with meanings and cases of their objects: https://forum.duolingo.com/comment/28544274
And here is a declension table for personal pronouns: https://forum.duolingo.com/comment/29119997
And just as a bonus, here's a declension table for noun endings:
Eventually, I will share my tables of possessive pronouns, determiners, etc., but it takes time to change the format into the table format for the mark-language used by Duo.
I found an interesting distinction in pronunciation concerning обо: at forvo.com, https://forvo.com/word/%D0%BE%D0%B1%D0%BE/#ru
обо by itself is pronounced with a stressed initial "o", so that it sounds like "oba" - but when couple with мне, the recorded Russian speakers say "aba mnye".