Meaning/Usage: To succeed at something; to arrive

In the literal meaning, to say a person arrived. But another common meaning is to say someone succeeded at something.

“You made it! I didn’t think you were going to show up.”

“I can’t believe you made it. It was a difficult task.”

“I made it in life”

“I made it” is used with a reference to a specific time, often implicitly now or today, and if you want to refer to something that happened in the past. For example, one would say “I made it” after climbing to the peak of a mountain, or when saying “I made it as a professional swimmer on 2 January 1982 when I won the gold metal.” 

“I have made it” is used without a specific reference to time. Thus, it means the event happened at some point in the past but the speaker isn’t being explicit about time. You are telling someone that, in the grand scheme of your life, you have done something.

For example, “I have made it as a professional swimmer”, means the speaker succeeded in becoming a professional swimmer but isn’t being specific about the time that he succeeded.

It’s a very subtle difference. Here are some more examples:

Today I challenged myself to run a mile, and I made it.

I have always wanted to swim across the river, and I’ve made it!

https://ell.stackexchange.com/questions/48310/i-made-it-vs-ive-made-it

http://www.talkenglish.com/lessondetails.aspx?ALID=1073