Learn Hardcore Korean: chinguwa badasga-e gayo. - I go to the beach with a friend.

와 is the comitative particle meaning with (or and) when attached to nouns ending in a vowel. In 친구와, it means “with a friend.” After a consonant-ending noun you’d use 과 instead. Note that 와/과 can also join two nouns as “X and Y.”

What is the difference between 바다 and 바닷가?

바다 means “sea” or “ocean.” The suffix 가 here is a native Korean bound noun meaning “edge” or “shore.” So 바닷가 literally means “seashore” or “beach.”

Why is the particle 에 used after 바닷가?

The particle 에 marks the destination or location for verbs of motion. Here, 바닷가에 = “to the beach.” If you wanted to say “at the beach,” you’d also use 바닷가에 있다 (exist at the beach).

Why is the verb 가요 in this form rather than 간다 or just 가?

가요 is the polite present tense form of 가다. You take the stem 가-, add -아요 (because 가 ends in a vowel), and then the polite ending 요: 가 + 아요 = 가요.

간다 is the plain (declarative) style often found in writing or informal speech among close friends.
가 is very casual (used with young children or very close friends).

Why is there no subject like “I” or “we” in the sentence?

Korean often omits subjects when they are obvious from context. In 친구와 바닷가에 가요, it’s understood that “I” (or whoever is speaking) am going. If you needed to be explicit, you could say 저는 친구와 바닷가에 가요 (“As for me, I’m going to the beach with a friend”).

Can we replace 친구와 with 친구랑 or 친구하고?

Yes. Both 랑 (more colloquial) and 하고 serve as comitative particles meaning with. So these sentences are all natural and mean the same thing:

친구랑 바닷가에 가요
친구하고 바닷가에 가요

Does 가요 ever express the future (like “will go”)?

Korean uses the present tense to describe near-future plans. So 내일 친구와 바닷가에 가요 literally means “(I) go to the beach with a friend tomorrow,” but in English it’s understood as “I will go to the beach with a friend tomorrow.” Time adverbs (like 내일) clarify the future meaning.