If I want to say that I was able to accomplish something, when should I say "I made it", and when should I say "I've made it"? What's the difference between the two forms?
Please give me a long answer to help me understand this correctly.
"I made it" is used with a reference to a specific time, often implicitly now or today. 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. 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.
I wouldn't ever use "I have made it on 2 January 1982." or even "I've made it yesterday." because those sentences include a reference to a specific time.
"I made it" -- You accomplished something. You would be telling someone about a specific time that you did something.
"I've made it" -- You didn't not accomplish something. You are telling someone that, in the grand scheme of your life, you have done something.
It's a very subtle difference. If you're specifically wondering about the verb "made", here are some examples:
Today I challenged myself to run a mile, and I made it.
I have always wanted to swim across the river, and now I've made it.
However, "to make it" in this sense is a strange idiomatic phrase where 90% of the time you would just say "I made it."
You can use in AE either made it or have made it for an action that has happened recently (in the recent past). For example:
However, if you want to refer to something that happened in the past, you use "made it". My father was a businessman. He made it big in business.
However, you use only "have made" (present perfect) in BE for a recent action and "made it" (past simple) for an action that occurred in the past.
I made it would generally be used when describing something you have done, i.e.:
Who made this cake?
"I made it"
You would say, I've made it while talking about being accepted into something, because:
Shrunk down so you would say something like:
Who made the basketball team?
I've made the basketball team!
what's missing from the above analysis is that "have made it" (specifically "Made It") is a phrase which has a specific cultural context in the West (especially America)
"Made It" is synonymous with "Achieved ___", usually "Achieved Success" (often wealth) or "Achieved the Good Life" (comfort, pleasure, ease, etc). This is based on the cultural assumption that Life is a climb up a "ladder" or mountain (or similar metaphor) leading to a better life, thus there is a top or pinnacle-- the "it" you've achieved. Western and American culture is FULL of metaphorical references to ladders, mountains, nirvanas at the top; "sliding down" because of mistakes or malice, etc.
Really, it's the presence of "IT" in this phrase that changes the meaning to a metaphor for life success.
In your example, "I've Made It" need not be the One Big Life Goal, but could be an intermediate goal-- for example, passing a class, finishing a marathon race. Or even, sarcastically, making it to the end of a tedious meeting or social obligation.
Thus, talking about "making it" ("I've made it") = "achieving success" is very different than "making _" = "constructing/building _".