Learn German: Guten Morgen! Ich trinke Kaffee. - Good morning! I am drinking coffee.

Morgen is a masculine noun. When you say Guten Morgen, it is actually a shortened version of "I wish you a good morning" (Ich wünsche dir einen guten Morgen). Because the morning is the direct object receiving the action in that hidden sentence, the adjective gut takes the masculine ending -en.

Does "Ich trinke" mean "I drink" or "I am drinking"?

It means both! Unlike English, German does not have a separate continuous tense (using "-ing"). Ich trinke translates to "I drink", "I am drinking", and even "I do drink" depending on the context.

Why does the verb "trinken" end in an "-e" here?

In German, verbs change their endings based on who is doing the action. The dictionary form of the verb is trinken (to drink). When the subject is ich (I), you drop the -en and add -e, making it ich trinke.

Why is "Kaffee" capitalized in the middle of the sentence?

In German, every single noun (a person, place, thing, or idea) is always capitalized, no matter where it appears in the sentence. Since Kaffee (coffee) is a noun, it must start with a capital letter.