"en drikk" is a noun. "å drikke" is a verb
EDIT: "drikke" might also be a noun. They are partially interchangable, given that you don't mean "drikke" as in "å drikke" (the verb).
It is more common to use "drikke" in a context such as "Jeg henter drikke" = "I'll get something to drink".
"En drikk" would be more suitable if you are refering to a specific type of beverage.
Example: "En drikk som Cola er usunn" = "A beverage such as Coke is unhealthy".
I have the same problem, since "ou" is Portuguese (my native language) for "or". "Elgen" is a bit difficult (and funny) as well because it sounds so similar to "alguem", which is Portuguese for "someone". And I'm not going to say a lot about "kjøtt" because I do not know if it would be appropriate, but it sounds like a bad word in Portuguese and every time it comes up when I'm with my family, they go like wtf.
I'm also a native Portuguese speaker and I have the same problem with "og"/"ou". However, I don't relate to the other two, and I am curious about what word is similar to "kjøtt" in Portuguese, I can't remember anything that resembles. Best of luck on your journey to learn norsk! :D