This is slightly confusing but here goes. In the infinitive you have the verb, "to come." The present tense is, "I come" adding an "s" for he, she and it. "Came" is the simple past tense. As such "I come" becomes "I came" if you are talking about coming in the past.
You can however also say, "I have come" which is known, confusingly, as the, "present in the past." You would use this to talk about a present state which has arisen as a result of a past action. So for example, "I have come a long way to be here." You are here now, in the present, but you got here because of an action which took place in the past.
What is Important to remember is that you can never say, "I have came" this is grammatically incorrect. It is, "I came" or, "I have come" and each are used in slightly different circumstances.