Welcome to the WP ecosystem ;D
At first I would recommend installing AppSwitch (
AppSwitch | Windows Phone Anwendungen + Spiele Store (Deutschland)) where you can search for the apps you used with Android and get suggestions for alternative apps in the WP Store or even find the same app.
Other suggestions:
WPCentral (must-have for all the news, tips, and reviews)
Weave News Reader
Weather, Health & Fitness, News ... from Microsoft (search for Bing in the Store
Tweet It! (Twitter)
Super Calendar
OneNote
Office Lens (should be awesome for your studies)
Metrotube (YouTube)
Messenger (Facebook Messenger)
Also be sure to check out (all) the apps in the Store's Nokia collection!!!