I'm having a hard time telling the difference in meaning between erlernt and gelernt. When I look them up in a GER-ENG dictionary, both translate to "learned". However, it seems that erlernt is used for the present perfect? Is gelernt used only for the past perfect then?
In this case the difference is not related to tenses. Erlernen and lernen are two different verbs.
More often than not er can be identified with a (non-separable) prefix that implies to do the things until the goal is reached ("Vorsilbe, die eine zielgerichtete Handlung ausdrückt"). Hence, erlernen is to learn something until you master it, while lernen might only be the process.
erlernen: sich lernend mit einer Sache beschäftigen, bis man sie beherrscht
You might wish to know something more here. E.g. erschießen means to shoot somebody dead, till the goal is accomplished (i.e. dies); while schießen can be only to shoot. Or ertrinken (drown); one "drinks" water till one dies.
My favorite is erinnern (to see into yourself until you find the thing you are looking for, till you remember).
Erlernen is an interesting derivation of lernen - or better a "specification". While lernen can be used to express learning pretty much anything, erlernen is almost exclusively used with regard to learning a skill or job and thus also implies a certain level of complexity of the subject that has been learned. (The term x-handwerk is also used very often in this context, implying that erlernen has a focus on manual/practical skill - though not exclusively)
Er ging nach Hamburg, wo er das Tischlerhandwerk erlernte.
He went to Hamburg where he learned/trained to become a carpenter.
Please note that it would sound weird to use erlernen with the actual job title/description in German, erlernen refers to the skill (carpentry, craftsmanship, etc.).
Erlernen in everyday spoken (and even written) German does sound quite anachronistic. As in the example I gave earlier, you are likely to find it in rather formal texts such as biographies or encyclopedia entries. Germans usually use lernen nowadays.
An interesting grammatical construction is how people tell you about the job/trade they learned nowadays. In the example I gave earlier erlernen was used in conjunction with the job/trade.
Er hat das Fleischerhandwerk erlernt
He learned to become a butcher
Today people would use lernen in conjuction with the job title, not the actual skill. Like this:
Ich habe Fleischer gelernt
I learned to be a butcher
"Er-" is a verb modifier that modifies the underlying verb. Even though it is not a preposition, it performs a similar role to prepositions such as an- auf- aus- that modify verbs when they are prefixes before a verb.
"Er-" is a modifier that means to "complete" or "fulfill." So lernen is the underlying verb for "to learn," and "erlernen" modifies it to "completely learn" (or "master.")
In any event, erlernen is not a "tense" of lernen; instead, erlernt is the past tense of erlernen. Gelernt is the past tense of lernen.
The meaning of "erlernen" is, that you mastered it yourself. A dog for example can't er-learn a trick, but he can learn it. You didn't er-learn your mothers tongue, because you didn't master it, it came naturally by listening to your parents for years. You plain learnt your language.
The same goes for all words with er-prefix:
erlernt erarbeitet erjagt erklettert erschlichen erbettelt erfochten erschmeichelt erlogen erträumt
It means that whatever you are talking about, didn't came naturally but you were the driving power behind it.