Jag minns inte titeln, men Anna sa att den började med ordet sommar.

In a normal Swedish main clause, the finite verb usually comes in second position, and inte normally comes after that verb.

So:

Jag minns inte titeln = correct

Not:

Jag inte minns titeln

This is a very important Swedish word-order rule.
A useful comparison:

• Jag minns inte titeln
• Anna sa att hon inte mindes titeln

In the second example, the clause after att is subordinate, and then inte comes before the main verb.

Minns is the present tense of minnas, which means to remember.

So:

• att minnas = to remember
• jag minns = I remember

Yes, you can also say kommer ihåg:

• Jag minns inte titeln
• Jag kommer inte ihåg titeln

Both are natural. Minns is a bit shorter and more compact; kommer ihåg is also very common in everyday speech.

Because Swedish uses a definite ending on the noun to mean the title.

• en titel = a title
• titeln = the title

So Jag minns inte titeln literally means I do not remember the title.

This is a basic Swedish pattern:

• en bok → boken
• en film → filmen
• en titel → titeln

Yes. Sa is the past tense of säga, meaning said.

• säga = to say
• sa = said

You may also see sade. Both are correct:

• Anna sa att ...
• Anna sade att ...

Sa is very common and natural in modern Swedish.

Here att means that and introduces a reported statement:

• Anna sa att den började ... = Anna said that it began ...

After verbs like säga, tro, veta, and hoppas, Swedish often uses att to introduce the next clause.

Learners sometimes want to leave it out because English can often omit that. Swedish can sometimes omit att too, especially in speech, but for learners it is safest and most natural to include it here.

Den refers back to titeln.

Since titel is an en-word, the pronoun is den:

• en titel → den

If the noun were an ett-word, you would usually use det instead.

So in this sentence:

• titeln = the title
• den = it, referring to titeln

Började is the past tense of börja, meaning began or started.

• börja = to begin, start
• började = began, started

The phrase börja med means begin with.

So:

den började med ordet sommar
means
it began with the word sommar

This is a very common combination in Swedish:

• Filmen börjar med en sång = The film begins with a song
• Mötet började med kaffe = The meeting began with coffee

Because the sentence is naming the exact word sommar.

After ordet, Swedish usually gives the word in its plain citation form:

• ordet sommar = the word sommar

If the title actually began with the specific word sommaren, then you would say:

• den började med ordet sommaren

So the form after ordet depends on the exact word being mentioned.

Also note:

• ett ord = a word
• ordet = the word

Because sommar is a common noun, not a proper name.

In Swedish, common nouns are not capitalized:

• sommar = summer
• bok = book
• titel = title

It is normal to write ordet sommar without capital letters. For extra clarity in teaching materials, people may highlight it with italics or bold, but ordinary capitalization is not needed.

The sentence has two main clauses, and the second one contains a subordinate clause.

Structure:

• Jag minns inte titeln = main clause
• men Anna sa = main clause
• att den började med ordet sommar = subordinate clause

That makes the whole sentence:

Jag minns inte titeln, men Anna sa att den började med ordet sommar.

This structure is useful to notice because Swedish word order changes depending on whether a clause is main or subordinate.