The difference in the two sentence structures is that of Voice. Or in other words, whether the doer of the action or the receiver of the action is the focus/protagonist of the sentence. The focus/protagonist of the sentence is called it's subject. It is basically just what or who the sentence is talking about. The rest of the sentence is called a predicate. For example, in case of "My parents gave me a special gift", the action being done is that of "giving" the doer of the action is "My parents" or just "parents" and the receiver is "me". The Subject of the sentence is also "Parents" because that is what the sentence is focussing on. And whatever is being said about "Parents" would be called a predicate. So, "gave me a special gift" is the predicate of the sentence. When the doer (in this case, "Parents")of the Action ("Gave") is the subject, the sentence is said to be in active voice. On the other hand In case of "I was given a special gift by my parents", the action is still that of "giving"; the doer is still "parents" or "My parents" for that matter, and reciever is also the same (the speaker of the sentence) but the focus or Subject of the Sentence has changed from "My parents" to "I", which is also the receiver of the action of "giving". When the receiver of the action is the subject, the sentence is said to be in Passive voice. I hope this clears your doubt. Do feel free to ask more questions.

मेरा शौक भाषाएँ हैं Is correct. but a more acceptable version. would be "भाषाएँ मेरा शौक हैं". You could also say "मुझे भाषाओँ का अध्ययन करना पसंद है"

I guess it is a cultural thing and has nothing to do with the language itself. So in conversation people try to put the other person at ease first by giving them a chance to talk about themselves or to gauge their willingness to have conversation and to give them space to open up. It certainly varies from person to person (amount of introversion or extroversion of the initiator or the receiver) and context.

आज <strike>मैं</strike> घर में रहकर <strike>पढ़ी</strike>। <strike>मैं</strike> हिन्दी का <strike>घर का पाठ</strike> करके <strike>कुछ</strike> पोलिश और जापानी भाषे <strike>सीखी</strike>। अब मैं कुछ <strike>कम</strike> करूंगी और उसके बाद मैं बाकी <strike>के</strike> दिन <strike>के लिए</strike> आराम करूंगी।

आज मैंने घर में रहकर पढाई करी। मैंने हिन्दी का गृहकार्य (homework) करके थोड़ी पोलिश और जापानी भाषाएं सीखीं। अब मैं कुछ काम करूंगी और उसके बाद मैं बाकी का दिन आराम करूंगी।