Translation:I teach because I like teaching.
Yeah well sometimes it's kinda tricky to literally translates something in Indonesian to English and the other way around, because the prefix and suffix and stuffs in Indonesian can change the meaning and form of an original word, so when you apply the prefix or suffix it can translate to different word in English.
Belajar and mengajar, both come from the original word "ajar". Ajar alone means teaching (noun), like for example: teaching books = buku ajar. or, teaching materials = bahan ajar. When ajar meets the prefix meng-, it changes the form of the original word from a noun to a verb, mengajar which means teaching (verb). When it meets the prefix be-, it forms another verb, which is belajar ("learn/study").