Keikka oli upea, ja haluan vielä tanssia.

In this sentence, keikka most naturally means a gig, show, or performance — especially something like a concert or live act.

It is a very common Finnish word in everyday speech. Depending on context, keikka can also mean other kinds of jobs or short work shifts, but here the idea is clearly an event or performance.

Oli is the past tense of on (is).

• keikka on upea = the gig is amazing
• keikka oli upea = the gig was amazing

So the speaker is talking about the performance as something already completed.

Because the two clauses refer to different times:

• Keikka oli upea: the performance is over, so past tense is used.
• haluan vielä tanssia: the desire exists now, so present tense is used.

This is completely natural in Finnish. The sentence is basically describing a past event and a current feeling about it.

If the speaker wanted to say the wanting was also in the past, they could say halusin instead.

Because upea is a predicate adjective after the verb olla (to be).

In Finnish, when an adjective comes after olla and describes the subject, it is often in the nominative singular if the subject is singular:

• Keikka oli upea.

So upea matches the singular subject keikka in this basic predicative structure.

Finnish often leaves out subject pronouns when they are already clear from the verb ending.

• haluan = I want
• haluat = you want
• haluaa = he/she wants

Because -n already shows first person singular, minä is not necessary.

You could say ja minä haluan vielä tanssia, but that would usually sound more emphatic, as if you want to stress I.

Vielä is a very common word with meanings like still, yet, more, or some more, depending on context.

Here it suggests something like:

• I still want to dance
• I want to dance some more
• I want to keep dancing

So it adds the idea that the desire continues, or that the speaker wants more dancing after what has already happened.

Because after haluta (to want), Finnish normally uses the first infinitive.

So:

• haluan tanssia = I want to dance
• haluan syödä = I want to eat
• haluan mennä = I want to go

Here tanssia is the dictionary/basic infinitive form of the verb tanssia (to dance).

Because haluta takes the basic infinitive directly.

• haluan tanssia = correct

Forms like tanssimaan are used with different verb patterns, especially verbs of movement:

• menen tanssimaan = I’m going to dance / I’m going dancing

So:

• haluan tanssia = I want to dance
• menen tanssimaan = I go to dance / I’m going dancing

They are different grammatical structures.

Because the sentence contains two clauses:

• Keikka oli upea
• (minä) haluan vielä tanssia

In Finnish, a comma is normally used between main clauses, especially when they have different subjects. Here the first clause has keikka as its subject, and the second clause has an understood minä.

So the comma is natural and standard here.

Yes, Finnish word order is fairly flexible, but changing it changes the emphasis.

The neutral version here is:

• Haluan vielä tanssia.

Other orders are possible, for example:

• Vielä haluan tanssia.
  This puts extra emphasis on vielä and sounds more marked or expressive.

• Haluan tanssia vielä.
  This is also possible, and can slightly emphasize the continuation or duration of the dancing.

So the original word order is the most neutral and natural one for a basic statement.

Because Finnish does not have articles like English a/an and the.

So keikka can mean:

• a gig
• the gig

The exact meaning depends on context.

That is very normal in Finnish, and learners have to get used to relying on context instead of articles.