If you're coming to Korea for the first time, the most important thing to do FIRST is learn the alphabet.
Even if you study absolutely no grammar or vocabulary, learning the alphabet is essential to your happiness and success in Korea. It's also the easiest part of Korean to learn. You can learn the entire alphabet in a single afternoon (or in a single blog post!).
Hangul has a total of 24 basic letters (less than the English alphabet).
The 24 basic letters can combine to form 40 total letters (less than Japanese).
TOTAL (40): Basic letters (24) + Double letters (16)
go (고), kimchi (김치)
big (빅), Visa (비자)
jam (잼), zero (재로)
pan, fan (팬)
*ㅎ: When in the final consonant position of one syllable, the sound carries over to the following syllable and aspirates it. For example:
ㄱ (g) → ㅋ (kk)
ㄷ (d) → ㅌ (t)
ㅂ (b) → ㅍ (p)
ㅈ (j) → ㅊ (ch)
*There are additionally a few other double consonants like 읽 and 없 but you can learn those as you come to them.
*ㅐ and ㅔ are nearly indistinguishable
+ ㅒ and ㅖ also sound the same
~ ㅙ, ㅞ, and ㅚ are also hard to tell apart
** There is no English equivalent for ㅢ. It is pronounced by combining those two vowels together "...e-uh...ee." (Although in some cases and dialects it is pronounced as ㅔ or ㅖ as in 나의 = "na-yay" or 그들의 = "ke-dul-ay".)