Tässä ovat kahvilat, joissa käymme viikonloppuna.

Tässä means here, and Finnish often uses tässä on / tässä ovat to present something that is being pointed out, shown on a map, listed, or physically indicated.

So Tässä ovat kahvilat... is very natural for Here are the cafés...

Nämä ovat kahvilat... would mean more literally These are the cafés... That is also possible in some situations, but it has a slightly different feel: it points to these ones, while tässä ovat feels more like here they are.

This is normal Finnish word order in a presentational sentence: first you give the place or setting, then the verb, then the thing being presented.

So:

• Tässä ovat kahvilat = Here are the cafés

This is similar to English Here are the cafés, where are also comes before the noun.

You could think of the structure as:

• Tässä = here
• ovat = are
• kahvilat = the cafés

Kahvilat is the plural nominative form of kahvila (café).

• kahvila = café
• kahvilat = cafés

It is nominative plural because it is the subject of the sentence: the things that are here.

Also, Finnish has no articles, so kahvilat can mean cafés or the cafés, depending on context.

Joissa is the plural inessive form of the relative pronoun joka.

Base form:

• joka = who / which / that

Plural:

• jotka = who / which / that

Inessive case (in):

• singular jossa = in which
• plural joissa = in which / where

So kahvilat, joissa käymme literally means:

• the cafés, in which we visit

but in natural English:

• the cafés where we go
• the cafés that we visit

Because the relative pronoun must take the case required by its role inside the relative clause.

Here the clause is:

• joissa käymme = where/in which we go/visit

The verb käydä when talking about visiting a place commonly uses the inessive case (-ssa/-ssä), meaning in/at.

So the pronoun cannot stay in plain plural nominative jotka. It must become joissa.

A useful way to see it:

• käymme kahviloissa = we go to / visit cafés
• therefore:
• kahvilat, joissa käymme = the cafés where we go

Because missä is mainly an interrogative or general adverb meaning where:

• Missä kahvilassa käytte? = Which café do you go to? / Where do you go?

In a relative clause after a noun, Finnish usually uses a form of joka instead:

• kahvilat, joissa käymme = the cafés where we go

So:

• missä = where?
• joissa = where / in which, referring back to kahvilat

In casual speech, Finns may sometimes use missä more loosely, but in standard written Finnish joissa is the expected form here.

Käymme is the we form of käydä.

• minä käyn = I go / I visit
• me käymme = we go / we visit

With places, käydä often means to go to, to visit, or to stop by.

So kahviloissa käydä is a very common Finnish way to say that you go to cafés or visit cafés.

It does not necessarily mean you literally walk in and out; it is just the normal verb for visiting a place in many contexts.

Because Finnish verbs already show the person.

• käyn = I go
• käyt = you go
• käy = he/she goes
• käymme = we go
• käytte = you (plural) go
• käyvät = they go

So käymme already includes the meaning we go.
You could add me for emphasis, but it is usually unnecessary:

• joissa me käymme = where we go

That sounds more emphatic, like contrasting we with someone else.

The ending -na / -nä is the essive case, and one of its common uses is expressing time when.

So:

• viikonloppuna = at the weekend / on the weekend / during the weekend

This is the same pattern as:

• maanantaina = on Monday
• kesällä is a different case, but also a time expression
• jouluna = at Christmas

So viikonloppuna answers the question when?

By itself, viikonloppuna usually suggests on the weekend / at the weekend, often referring to a specific upcoming or contextually known weekend.

If you want a clearly habitual meaning, Finnish often uses -isin:

• viikonloppuisin = on weekends / at weekends

So there is a small difference:

• käymme viikonloppuna = we go on the weekend
• käymme viikonloppuisin = we go on weekends, habitually

In context, though, viikonloppuna can sometimes still be understood more generally.

Finnish has no articles like a, an, or the.

So kahvilat can mean:

• cafés
• the cafés

The context tells you which one is intended. In this sentence, English would usually use the cafés, but Finnish does not need a separate word for that.

Yes. Historically and grammatically, tässä is the inessive form of tämä.

• tämä = this
• tässä = in this / here

In modern use, tässä often simply means here.

That is why Finnish learners often notice that many location words are really case forms:

• tässä = here
• siinä = there
• tuossa = there (near you / that one there)

It would be:

• Tässä on kahvila, jossa käymme viikonloppuna.

Changes:

• ovat → on because the subject is singular
• kahvilat → kahvila
• joissa → jossa because the relative pronoun must match the singular noun

So:

• kahvila = café
• jossa = in which / where

In standard Finnish, no. Since kahvilat is plural, the verb should also be plural:

• Tässä ovat kahvilat...

Using singular on with plural kahvilat would sound nonstandard here.

So the agreement is:

• kahvila → on
• kahvilat → ovat