-i type suffixes are the suffixes that have the ı, i, u, ü versions.

Vowel harmony rules in -i type suffixes: 

If the last vowel is "a, ı" the suffix will be the -ı version

If the last vowel is "o, u" the suffix will be the -u version

If the last vowel is "e, i" the suffix will be the -i version

If the last vowel is "ö, ü" the suffix will be the -ü version

Examples to -i type suffixes:

-mı, mi, mu, mü (question suffix)

-ıyor, -iyor, -uyor, -üyor, (Present Continuous Tense suffix)

-dı, -di, -du, -dü, (Simple Past Tense suffix)