I realized there are many posts on this student blog already, so I thought of doing a “short listing” to make easier for you to find what you are interested in:
Life in Uppsala. On this Facebook page there are plenty of insights about activities, accomodation, and living in Uppsala as a student: https://www.facebook.com/studysustainably/
What’s ECM about? I made a post in April 2018 for those accepted this year. I recommend you to read it because I make a distiction between Environmental or Social Sciences?, and comment about the activities and lectures. If you read other posts you will realize that there is a mix between social theory, discussions, and practice through activities such as research in groups, role plays, presentations, group assignments… etc.
Internship: Details about where students did their internship are mainly on September 2018 posts; Students have to search and apply for their own internship. This is not a big deal, I think, because we do interviews for research assingments over the first year, as well as we hear about where we could do our internship from lectures, guest lecturers… so there are plenty of people you can contact again if you are interested.
Master Thesis: The topic is your own choice, and EC students do not need to approach researchers. Instead, there is a “guarantee” that you will get a supervisor matching your topic of interest. (But I think you can search your own in other university if you prefer that). Posts about the thesis are on this year 2018-2019.