1) What does the word tanwīn mean?
It means to make the sound of the letter nūn after the word. Notice that when a word like bayt has a tanwīn on the end, it will be pronounced as baytun or baytan or baytin. The -n sound on the end is what the tanwīn signifies.
2) Are there any tips for memorizing the sun and moon letters?
One tip is that the sun letters in the Qur’an always have a shaddah written on the letter after the alif lām, whereas the moon letters will not. Using this tip you will eventually memorize which ones are which.
3) Are there conjugations in English?
English has a very basic conjugation system. We would say “He says” as opposed to “We say.” This is a basic English conjugation. The difference between Arabic and English is that Arabic has a unique conjugation pattern involving adding prefixes and suffixes to the root verb for each tense and each pronoun that is being used in that tense. For example, the word “says” in “He says” and “She says” would sound different in Arabic.