There are two kinds of adjectives, true and false (pseudo-adjectives).
True adjectives end in -i whereas false adjectives... well, don't necessarily. However, it is possible for pseudo-adjectives to end in -i also.
True adjectives include words like kawaii, muzukashii (cute and difficult)
Hen, heta, kantan (weird, bad (as in unskilled, not "a bad person") and simple) are examples of false adjectives. Aside from the pretty obvious -i ending the main difference is that pseudos need "na" between the adjective and the noun to make sense.
You can say "kawaii neko desu", but not "hen hito". The proper version of the latter would be "hen
na hito."
And if anything needs any additions or corrections, please come with them. I'm still pretty new in the game myself, but I think this should be about right. I hope I haven't made any glaring mistakes here, that could be a little embarrassing.
