i- adjectives ans na-adjectives in japanese

ok im slightly confused as to which of these to use when describing something.
the examples i have seen show
aka-i (red)
kirei-na (pretty)

taka-i yama (a high mountain)
kirei-na hana (a pretty flower)

Im confised as to which i use at which situations.

please someone explain this to me.

>>3
True.

>>5
Maybe he's writing from u"nterdevice, without proper input methods? (just like my PC on work and phone)


>>Disregarding that<<
Where is our traditional "日本語 Ask a question thread"?