SPEECH LEVELS
There are many speech levels in Korean, but these are the main ones.
FORMAL LEVEL
You'll use it to talk to your boss, elder people, sometimes your older parents, your teacher, etc.
Basically, you need to do is removing both the -아/-어 and the -요 particle from the polite level. Then you'll add -습니다 if the verb ends with a consonant and -ㅂ니다 if it ends with a vowel.
REMEMBER THAT some words change in formal levels, like 나 → 저. f you need to make 저 into a subject, it will become 제가.
POLITE LEVEL
It is commonly used when you don't know someone very well but generally, it is good in almost every situation (use it and you'll be sure 99% not to ever go wrong).
It is the level we always use for examples, so you should know it already!
INFORMAL LEVEL
You'll only use this level with close friends, your family, or someone who directly allowed you to use it.
It is built by removing the -요 particle from the polite verb.
REMEMBER THAT sometimes the - 는 or -를 markers are involved in the noun they're related to.
Eg:
나는 → 난
나를 → 날
너는 → 넌
너를 → 널