Indonesian gave you no conjugation, no gender, no articles and no tenses. It takes payment in one place, and this is it.
One root, many words
Take ajar, the root meaning teach. On its own you rarely see it. Wrapped in affixes it becomes:
belajar ‘to study’
mengajar ‘to teach’
ajaran ‘a teaching, a doctrine’
pelajar ‘a student’
pelajaran ‘a lesson’
pengajar ‘a teacher’
Six words, one root. A dictionary lists them separately and a learner memorises them separately, which is six times the work for no reason.
The trick is seeing the root
Indonesian words look long and unfamiliar until you can strip them. Once you can, a word you have never met becomes a word you can guess.
membersihkan is bersih ‘clean’ with mem- and -kan around it: to clean something.
keindahan is indah ‘beautiful’ with ke- and -an: beauty.
That is the entire skill. Everything else in this level is learning what each wrapper does.
The cast
Prefixes, in front:
ber- mostly intransitive, having or doing
me- active verbs, and the shape changes with the letter it meets
di- passive
ter- accidental, or superlative
pe- the person or thing that does it
ke- mostly with -an, makes abstract nouns
Suffixes, behind:
-kan makes a verb take an object, or causes something
-i also takes an object, differently
-an makes a noun
And they combine. ke-…-an, pe-…-an, me-…-kan, di-…-kan. Most long Indonesian words are a root with a prefix and a suffix.
The order you will meet them
This level covers ber-, me- in outline, di- and ter-. The B1 level takes me- apart properly, including the sound changes, and then handles -kan against -i, which is the hardest single thing in the language.
Do not try to learn them all now. Learn to see the root, and the rest arrives in order.
The spelling change to expect
Affixes change shape to fit the word. ber- + ajar is not berajar but belajar. me- + tulis is not metulis but menulis.
These changes are regular and they follow the sound, not the spelling. They are the reason me- gets a whole chapter later rather than a paragraph now.