If you want take full control of your keyboard like a programmable keyboard, KE is the thing.
If you only want do some dead simple remap, Alfred is one of the choices but not the most advanced.
KE only do key-map things, it's not a replica of Alfred.
Read the Official Documentation:
https://karabiner-elements.pqrs.org/docs/
It is the best way to understand how it works and how you config your keyboard.
You can learn from other people's config files:
https://ke-complex-modifications.pqrs.org
There is even an DSL exists for writing KE config files(for advanced config):
https://github.com/yqrashawn/GokuRakuJoudo
Goku can generate 10000+ lines of KE config files from only hundreds lines.