1.) Usage of "geliyorum" : it means="I'm coming". But you will experience it is used when we are actually "going"! For instance you are sitting in living room with your friend and he stands up to go to kitchen to have a glass of water. When he stands up he would say "geliyorum-I'm coming" even tough going, here the underlining meaning when we use "coming" in the place of "going" is "going for a very short time", it's like I'm almost back ,or popping to kitchen.
2.)Tense difference comparing to English
The following meanings are made in English in past tense whereas in Turkish we use them in present;
(present tense)I understand=Anladım (past tense)
(present tense) Coming=Geldim (past tense)
3.) Similar verbs; Very easy to get confused cause they only have one letter difference;