Learn Hardcore Finnish: Kurssin alussa olin vielä aika epävarma. - At the beginning of the course I was still quite unsure.

[GENITIVE] + [a noun in a local case]
kurssin alussa = at the beginning of the course
vuoden lopussa = at the end of the year
tunnin aikana = during the lesson

So kurssi alussa would be ungrammatical in this meaning; you need the genitive kurssin.

Why is alussa used? What’s the difference between alussa, alusta, and alkuun?

All three come from alku (beginning), but the case changes the meaning:

alussa (inessive) = in/at the beginning
- Static location or time point
- Kurssin alussa = at the beginning of the course
alusta (elative) = from the beginning
- Movement or starting point, often with “from”
- Aloita alusta = start (again) from the beginning
alkuun (illative) = to the beginning / at first
- Movement towards, or initial phase of something
- Alkuun se oli vaikeaa = at first it was difficult

In your sentence we’re talking about the situation at that initial phase of the course, so alussa is the natural choice.

Why is it olin and not minä olin? Is the subject pronoun always dropped?

Finnish usually drops the subject pronoun when the verb ending already shows who the subject is.

olin = I was
olit = you were
olimme = we were

Because olin can only mean I was, minä is not required.

Both are correct:

Kurssin alussa olin vielä aika epävarma.
Kurssin alussa minä olin vielä aika epävarma.

Using minä adds emphasis to I, e.g. contrasting with someone else:

Kurssin alussa minä olin vielä aika epävarma, mutta muut eivät olleet.
= At the beginning of the course I was still quite unsure, but the others weren’t.

What exactly does vielä mean here?

Vielä usually means still, yet, or even, depending on context.

In this sentence it means still:

You were already on the course, but your feeling of uncertainty continued at that time.

Nuance-wise, vielä suggests that:

the situation had been like that earlier, and
it might change later (you may become more sure of yourself).

Some quick comparisons:

Olen vielä väsynyt. = I’m still tired.
En vielä tiedä. = I don’t know yet.
Se on vielä parempi. = It’s even better.

What does aika mean here? I thought aika means time.

You’re right that aika most often means time:

Minulla ei ole aikaa. = I don’t have time.

But here aika is an adverbial intensifier meaning quite / rather / pretty:

aika hyvä = quite good / pretty good
aika vaikea = rather difficult
aika epävarma = quite unsure

This aika is very common in spoken and informal written Finnish. It’s softer and more casual than some other intensifiers:

melko epävarma = fairly / rather unsure (a bit more neutral/formal)
todella epävarma = really unsure
erittäin epävarma = extremely / very unsure (formal/strong)

What does epävarma literally mean, and how is it formed?

Epävarma is an adjective meaning unsure / uncertain / not confident.

It’s built from:

varma = sure, certain, confident
epä- = a negative prefix (like un-, in-, non- in English)

So literally: epä + varma ≈ unsure or not sure.

Other common epä- words:

epäkohtelias = impolite (kohtelias = polite)
epätodennäköinen = unlikely (todennäköinen = likely)
epäselvä = unclear (selvä = clear)

In your sentence, epävarma is a predicative adjective describing the subject minä (implied):

(minä) olin epävarma = I was unsure

Why doesn’t epävarma change its form? Shouldn’t adjectives agree with the subject?

They do agree, but here the agreement is “invisible” because both the subject and the adjective are in nominative singular.

The (implicit) subject is minä (I), which is nominative singular. The predicative adjective also takes nominative singular:

Minä olen väsynyt. (I am tired.)
Sinä olet väsynyt. (You are tired.)
Hän on väsynyt. (He/She is tired.)

When the subject is plural, the predicative adjective usually becomes plural nominative too:

Me olemme epävarmoja. = We are unsure.
- epävarma → epävarmoja (plural partitive form used as predicative here)

In your sentence it’s singular I, so epävarma stays in its basic form.

Why is the past tense olin used instead of something like olen ollut?

Olin is the imperfect (simple past) of olla (to be). It describes a state in the past, seen as a whole:

olin epävarma = I was unsure (at that time)

Olen ollut is the perfect tense:

olen ollut epävarma = I have been unsure

The difference:

Kurssin alussa olin vielä aika epävarma.
= Describes how you felt at that specific period in the past.
Kurssin alussa olen ollut aika epävarma.
= Grammatically possible, but sounds odd; perfect usually connects past to the present.
It would suggest your uncertainty starting then and being relevant now, which doesn’t fit well with a clear past time expression (kurssin alussa).

In Finnish, a clear time expression referring to a finished time (yesterday, last year, at the beginning of the course, etc.) normally goes with the imperfect, not the perfect.

Can the word order of vielä and aika change? For example, is olin aika vielä epävarma correct?

The natural word order is:

olin vielä aika epävarma

Here’s why:

vielä (“still”) modifies the whole state: I was still…
aika (“quite”) modifies the adjective epävarma

So the structure is:

[verb] + vielä + intensifier (aika) + adjective

Other acceptable variants (slight nuance changes, but still fine):

Olin aika epävarma vielä kurssin alussa.
Kurssin alussa olin aika epävarma vielä. (more spoken, and vielä feels slightly emphasized)

But:

olin aika vielä epävarma
sounds unnatural; aika normally comes directly before the adjective it intensifies (epävarma).

What is the base form of kurssin, and how does this genitive form work?

The base form (nominative) is kurssi (course).

The genitive singular is kurssin:

If the word ends in -i, you often (not always) get -in in the genitive:
- kurssi → kurssin
- kieli → kielen
- lasi → lasin

Here kurssin marks a possessive/relational link to alku:

kurssin alku = the beginning of the course
kurssin alussa = in the beginning of the course

This pattern is extremely common:

kirjan nimi = the book’s title / the title of the book
elokuvan lopussa = at the end of the movie
tunnin lopussa olin väsynyt. = At the end of the lesson I was tired.