How do I become good with functional features(map,reduce,filter,zip,flatmap) in Javascript and Python?

It feels so alien. I'm so used to writing plain old loops.
Reading and undersranding this kind of style in other people's code is really hard for me, especially if all this is happeining on the same line.

Maybe you people will like this story.
The past semester I studied Java in class. First time doing object oriented programming, I had an annoying teacher but got the hang of it. I still miss C from the last year.
As a final project we had to do any program and apply some stuff we saw in class (The program should have an array list, use interfaces, bla bla bla bery simple stuff). It also must have a complete documentation, a manual and a diary explaining what was developed every week. Bonus points if it was in a repository like GitLab.
I wanted to do an RPG game in a matrix, like a rougelike or an old FF game, that should be a map or two, a few monsters and items and that's it. Enough to show what can I do and to have enough excuses to apply everything that the teacher asked. I had a team with two friends who wanted to do the same.
After making accounts in three different pages that apparently would help us to be more organized (One to make charts and two task trackers) I lost all patience and made an account in GitLab, made the basic classes that we had defined in a chart, divided the tasks and put them in to do on GitLab and we started to work.
One of my companions caused a lot of problems. First, he didin't wanted to learn how to use GitLab (I simply asked them to do merge requests) and he insisted to use GitHub. Then he started to say that using the console version was even better (Pretty sure he said thet he never used Git, but maybe was gas poisoning). The GitLab repository never had a single commit to his name.
BUT WAIT IT GETS BETTER all the entire time, he was complaining about the graphical interface of the game, wanting to use some SDK for RPGs that he found. I told him that we will see that at the end, that first we should have all the mechanics done, test it in ASCII in the console and then, if we have time, we will put the visual interface, separated and optional from the main program to avoid problems.
After two weeks where he gave me very simple standard stuff late, half done and through Google Drive, I discovered he was most of the time working on... the graphical interface SDK! He took the job already done by me and the other guy and making a pretty hardcoded integration with the graphical interface and making everything that he tought it would be necesary. Soon enough the GitLab repository was totally outdated and completly useless. He had the totallity of the project in his half broken laptop, and sometimes he gave us a zip with all the code, outdated after a few minutes. Most of the stuff that I made was modified, a lot of the code was totally unknown to what it was and I had no idea even of how the folders were organised.
We had a month to finish it. I got totally disconected from the project and just hoped for the best, sometimes doing a handful of generic and adaptable lines of code for a specific thing (Funny enough, many core mechanics were nonexistent). The other guy managed to work more on the project, mostly fixing the mess that the guy did: apparently he didin't read the documentation of the SDK and just experimented and saw tutorials and tried to figure out how to do what he wanted.
Talking about documentation: we dont had yet. The code wasn't even commented propely. We did all that the last week and some stuff was finished the last night. The program apparently worked but I had no idea.
Thank God, the teacher just looked over everything and was very impressed by the working camera and the FF tiles. I don't think he saw the code or read too much of the documentation, much less when I directly wrote how I lost all access to the project.
I had a 10/10. I didin't complained. Most easy and annoying ten I ever had. I will never do a project with that guy.