Meine Oma sagt, ein bisschen Zimt passt auch gut zu warmen Blaubeeren.

Because in German, all nouns are capitalized.

• Oma = grandmother / grandma
• Zimt = cinnamon
• Blaubeeren = blueberries

That is why they start with a capital letter, even in the middle of the sentence.

Oma is the normal, affectionate everyday word for grandma.

• meine Oma = my grandma
• meine Großmutter = my grandmother

Großmutter sounds more formal or neutral. In family speech, Oma is much more common.

German uses commas to separate clauses more regularly than English does.

Here you have:

• Meine Oma sagt = main clause
• ein bisschen Zimt passt auch gut zu warmen Blaubeeren = the clause telling you what she says

So the comma is required.

Because the second clause is written without dass.

German often allows both versions:

• Meine Oma sagt, ein bisschen Zimt passt auch gut zu warmen Blaubeeren.
• Meine Oma sagt, dass ein bisschen Zimt auch gut zu warmen Blaubeeren passt.

Without dass, the clause keeps normal main-clause word order, so passt stays in second position.

With dass, the verb goes to the end.

Because the subject is ein bisschen Zimt, and that is treated as singular.

So:

• ein bisschen Zimt passt
• not ein bisschen Zimt passen

Even though Blaubeeren is plural, it is not the subject. It is part of the phrase after zu.

Ein bisschen means a little or a little bit of.

So:

• ein bisschen Zimt = a little cinnamon

It is very common with uncountable things like:

• ein bisschen Salz
• ein bisschen Wasser
• ein bisschen Zucker

A close alternative is etwas:

• etwas Zimt

Both work, but ein bisschen often sounds a little more conversational.

Here passen zu means to go well with or to suit.

So:

• Zimt passt zu Blaubeeren = cinnamon goes well with blueberries

This is a very common German structure:

• Der Wein passt gut zum Käse.
• Rot passt nicht zu Grün.

The preposition zu is an important part of the expression.

Because zu always takes the dative case.

And here Blaubeeren is plural, so the adjective must be in dative plural:

• zu warmen Blaubeeren

That is why you get warmen.

A similar example:

• zu frischen Erdbeeren
• zu kalten Getränken

So the key idea is:

• zu
  • dative
• plural adjective in dative = often -en

Because both are being used in a general way.

• Zimt is a mass noun, like cinnamon in English, so no article is very normal.
• warmen Blaubeeren refers to warm blueberries as a kind of dish or ingredient, not a specific previously mentioned set.

So this sounds natural:

• Zimt passt zu Blaubeeren.

If you meant specific blueberries, you could say:

• ... zu den warmen Blaubeeren.

That would mean to the warm blueberries already known in the situation.

Auch means also or too.

So passt auch gut means also goes well.

The idea is that cinnamon is being added as another good option.

Sentence feeling:

• my grandma says that a little cinnamon is also good with warm blueberries

So maybe some other ingredient has already been mentioned, and cinnamon is one more suggestion.

Yes, and moving auch can slightly change the emphasis.

Compare:

• Ein bisschen Zimt passt auch gut zu warmen Blaubeeren.
  = A little cinnamon also goes well with warm blueberries.

• Auch ein bisschen Zimt passt gut zu warmen Blaubeeren.
  = A little cinnamon too goes well with warm blueberries.

The difference is subtle, but in German word position often affects what is being emphasized.

In your original sentence, auch most naturally adds the idea that cinnamon is another thing that works well.