Vi samlar in pengar till ett gott ändamål.

Because samla in is a fixed verb expression meaning to collect or to gather in, especially when talking about things like money, signatures, or information.

• samla = gather, collect
• samla in = collect in, gather in, raise/collect (for a purpose)

So:

• Vi samlar pengar can sound like we collect money
• Vi samlar in pengar is the more natural phrasing for we are collecting money / raising money

In this sentence, samlar in works like a separable verb, which is why the two parts are split up.

This is very common in Swedish with certain verbs that include a particle, like in, ut, upp, and so on.

In a main clause, the finite verb usually comes early in the sentence, and the particle often stays later:

• Vi samlar in pengar.

Compare with the infinitive form, where they stay together:

• att samla in pengar = to collect money

So:

• Vi samlar in pengar = main clause
• Vi vill samla in pengar = infinitive after another verb

This is similar to English phrasal verbs like pick up:

• We pick up the box
• We want to pick up the box

Pengar means money in a general sense here, not the money.

• pengar = money
• pengarna = the money

So:

• Vi samlar in pengar = We are collecting money
• Vi samlar in pengarna = We are collecting the money

The second version would suggest specific money that has already been mentioned or is known from context.

In Swedish, pengar is the normal word for money, and it is grammatically plural in form.

You will often see plural agreement around it:

• Pengarna är här. = The money is here.

Even though English treats money as an uncountable singular noun, Swedish uses pengar, historically related to coins or units of money.

So this is something you mostly just learn as a vocabulary fact:

• English: money
• Swedish: pengar

Here, till means for in the sense of for the benefit of or for the purpose of.

So:

• pengar till ett gott ändamål = money for a good cause

Swedish till has several meanings depending on context, including to, for, or until, but in this sentence it is clearly for.

Other examples:

• pengar till barnen = money for the children
• ett bidrag till projektet = a contribution to/for the project

Ändamål means purpose, aim, or cause, depending on context.

In the phrase ett gott ändamål, it is best translated as a good cause.

Word-for-word, though:

• ett = a
• gott = good
• ändamål = purpose / cause / end

So the phrase literally suggests a good purpose, but in natural English a good cause is the best match.

This is a somewhat formal or standard expression. You will often hear:

• till ett gott ändamål = for a good cause

Because ändamål is an ett-word (a neuter noun), not an en-word.

In Swedish, adjectives change form depending on the gender of the noun.

• en word: en god sak
• ett word: ett gott ändamål

So here:

• ändamål is neuter
• therefore the adjective god becomes gott

This -t ending is very common with ett-words in the singular indefinite form.

More examples:

• ett stort hus = a big house
• ett bra förslag = a good suggestion
• ett gott råd = a good piece of advice

It is partly predictable, but god is a little special.

For many adjectives, you simply add -t for an ett-word:

• stor → stort
• liten → litet

With god, the neuter form is gott, not godt.

So yes, that specific spelling and form should be learned as an irregular pattern:

• en god idé
• ett gott ändamål
• goda vänner

This adjective is very common, so it is worth memorizing its forms.

A learner might expect för because English says for a good cause, but Swedish idiom prefers till in this expression.

The phrase samla in pengar till ... is very natural Swedish:

• Vi samlar in pengar till forskning.
• De samlar in pengar till välgörenhet.

Using för is not always impossible in Swedish, but with this structure, till is the normal choice.

A good rule here is:

• learn samla in pengar till något as a chunk

It is present tense, and in Swedish the present tense often covers both:

• we collect money
• we are collecting money

So Vi samlar in pengar can mean either, depending on context.

Swedish does not usually need a separate am/is/are + -ing form the way English does.

Examples:

• Jag läser. = I read / I am reading
• De arbetar. = They work / They are working

So here, the sentence can naturally mean We collect money or We are collecting money, depending on the situation.

A more literal breakdown would be:

• Vi = we
• samlar in = collect / gather in
• pengar = money
• till = for
• ett gott ändamål = a good cause / a good purpose

So a fairly literal version would be:

We collect money for a good cause.

Or, staying slightly closer to the Swedish structure:

We are collecting money for a good cause.

That is both natural English and a good guide to the Swedish sentence structure.