Blanda kortleken före första omgången.

Here it is the imperative. For many Swedish verbs ending in -a, the imperative has the same form as the infinitive:

• infinitive: att blanda
• imperative: blanda!

So the form looks the same, but the context tells you which one it is.

Swedish uses compounds very freely, so English deck of cards becomes the single word kortlek.

Then -en is the definite ending:

• en kortlek = a deck of cards
• kortleken = the deck of cards

So kortleken means the deck.

Because Swedish usually marks definiteness by adding it to the end of the noun.

Compare:

• en omgång = a round
• omgången = the round
• en kortlek = a deck
• kortleken = the deck

English uses a separate word, the. Swedish often uses a suffix instead.

Före means before and is very natural before a noun phrase:

• före första omgången = before the first round

Innan is also common, but it is especially common before a clause:

• innan spelet börjar = before the game starts

You may hear innan första omgången too, especially in speech, but före första omgången is very standard in instructions.

Also, do not confuse före with för:

• före = before
• för = for

Because Swedish often uses a definite noun after ordinal numbers when referring to a specific one:

• första omgången = the first round
• andra dagen = the second day

So första omgången is the normal way to say the first round.

Both patterns exist in Swedish, but with ordinal numbers, Swedish often leaves out den/det/de, especially in short instructions and set phrases.

So these can both be possible:

• före första omgången
• före den första omgången

In a sentence like this, före första omgången sounds very natural and concise.

In games, omgång means round. It is a common word for one stage or cycle of play.

Depending on context, omgång can also mean a round in a competition, betting round, or similar repeated phase. In this sentence, it simply means the first round of the game.

Yes, often you can. Both are natural, but they emphasize slightly different things:

• Blanda kortleken = shuffle the deck
• Blanda korten = shuffle the cards

In practice, both can work in a card-game instruction. Kortleken focuses on the deck as one set. Korten focuses on the cards themselves.