Learn Hardcore Korean: cheoeumieoseo jogeum ginjangdwaeyo. - Because it’s my first time, I’m a little nervous.

It’s the connective “because (it) is.” Grammatically, 이다 + -어서 → (이)어서, so 처음이어서 means “because it’s the first time.” You can also say 처음이라서; both are correct and mean the same thing. In everyday speech, -(이)라서 is a bit more common, while -(이)어서 can feel a touch more formal or careful. Here, both sound natural.

Can I just say 처음이라(서) without the -서? For example, 처음이라 조금 긴장돼요?

Yes. Dropping -서 is common and natural in speech: 처음이라 조금 긴장돼요 is fine. The meaning remains “since/because it’s my first time.” With or without -서, it conveys a reason; including -서 can feel slightly more explicit or formal.

Why use 긴장돼요 instead of 긴장해요?

긴장되다 expresses an involuntary, passive-like feeling: “I (end up) feel nervous.”
긴장하다 is the active verb “to be tense/to tense up,” which can sound a bit more deliberate or controlled. Both are used, but when describing a natural, uncontrollable feeling in a new situation, 긴장돼요 is the most idiomatic. Another common option is 떨려요 (“I’m jittery/nervous”).

Is 긴장돼요 a passive form?

Yes, morphologically it’s the 되다 counterpart of a 하다-verb pair (긴장하다 ↔ 긴장되다). In practice, 긴장되다 doesn’t feel like an English passive; it simply means “to feel/become nervous” without implying an agent causing it.

How do I spell and pronounce 돼요? Why is 되요 wrong?

Spelling: 되 + 어요 → 되어 → 돼요. So write 돼요, not 되요.
Pronunciation: usually [dwae-yo] (often sounds like [dwe-yo] in modern speech).
Related forms: 됐어요 (past; from 되었어요), 돼서 (from 되어서). Avoid the common misspelling 됬어요.

How is the whole sentence pronounced naturally?

처음이어서: roughly “cheo-eum-ieo-seo” (the ㅁ links smoothly to 이).
조금: “jo-geum” (often reduced to something like “jo-kkeum” in fast speech).
긴장돼요: “gin-jang-dwae-yo.” Said together: “cheo-eum-ieo-seo jo-geum gin-jang-dwae-yo.”

Do I need to say 저는 or 제가?

No. Subjects are often omitted when clear from context. You can add them for emphasis or clarity:

저는 처음이어서 조금 긴장돼요. (I’m the one who’s new, so I’m a bit nervous.)
제가 처음이라서 조금 긴장돼요. (Emphasizes “I” in contrast to others.)

Can I use 처음으로 or 처음에 instead of 처음이어서?

They’re different:

처음으로 = “for the first time” (adverbial): 오늘 처음으로 발표해요.
처음에 = “at first/at the beginning”: 처음에 조금 실수했어요.
처음이어서/처음이라서 = “because it’s (my) first time.” Use this for the cause in your sentence.

What’s the difference between 처음, 첫, and 첫째?

처음: noun/adverb meaning “first time/at first.” Can stand alone: 처음이에요.
첫: prenoun (attributive) meaning “first”: 첫 경험, 첫 인상. It cannot stand alone.
첫째: ordinal “first (in order/rank)” or “firstly.”

Is 조금 the same as 좀 or 약간 here?

조금 and 약간 both mean “a little/a bit.” 조금 is neutral; 약간 can feel slightly formal or objective.
좀 is a colloquial contraction of 조금 and also works as a softener. In your sentence, 조금 or 좀 both sound natural: 조금/좀 긴장돼요.

Can I say 긴장돼 있어요 or 긴장하고 있어요?

긴장돼 있어요 is usually awkward.
긴장하고 있어요 is possible, but it emphasizes the ongoing act of being tense. For a simple “I feel nervous,” 긴장돼요 is the most natural.

How do I change the tense or talk about future/likelihood?

Past: 처음이라서 조금 긴장됐어요.
Future/likelihood: 처음이라서 조금 긴장될 것 같아요., 처음이라서 아마 긴장될 거예요. Note: Don’t say 처음이었어서 for a reason clause; keep the reason in the (present) -(이)라서/-(이)어서 form and put tense on the main verb: 처음이라서 긴장됐어요.

Could I use -(으)니까 instead of -(이)어서/-(이)라서?

Yes: 처음이니까 조금 긴장돼요. Both mean “because/since,” but:

-(으)니까 is more speaker-judgment/volition and is preferred when making requests/commands: 처음이니까 천천히 해 주세요.
-아서/어서 (including -(이)라서) often states a factual cause.

Is 긴장돼요 one word? Can I also say 긴장이 돼요?

긴장되다 is a dictionary verb, so 긴장돼요 is one word.
You can also use the noun + subject marker: 긴장이 돼요. Both are acceptable and common (same with 걱정(이) 돼요). The one-word form is slightly more compact.

Does 이어서 ever mean “next/then”? Is that what it is here?

There is an adverb 이어서 meaning “(right) after/next/in succession,” as in 발표가 끝나고 이어서 질의응답이 있겠습니다. That is a different word. In 처음이어서, 이어서 is the connective from 이다 + -어서 meaning “because (it) is.”