You now have all the single Korean consonants. As you learn more Korean, you may see words like these:
젊다 or 젊어서
What’s going on here? Up until now we've had only one consonant “in the basement.” All of a sudden we’ve shoehorned two consonants ( ㄻ) into the bottom of the syllable.
This is called a consonant cluster. Here’s the general rule: if the syllable following a cluster starts with a vowel sound, the second consonant attaches itself to the vowel; that means you pronounce:
젊어서 as if it were 절머서
If there’s a consonant starting the syllable after the cluster, well, there’s a whole bunch of rules that tell you what to do. The usual result is that only one of the two consonants is pronounced, and the other one vanishes.
My advice for now: recognize that consonant clusters exist, and consult a good book or a good teacher if you need to know the pronunication rules.