Lägg spelpjäsen på spelplanen.

Because Swedish very often makes compound nouns by joining words together.

• spel = game
• pjäs = piece/token

So:

• spelpjäs = game piece / playing piece

English often writes these as separate words, but Swedish usually writes them as a single word.

The same thing happens in:

• spelplan = game board
• spelplanen = the game board

In Swedish, the definite article is usually added to the end of the noun instead of appearing as a separate word before it.

So:

• en spelpjäs = a game piece
• spelpjäsen = the game piece

and

• en spelplan = a game board
• spelplanen = the game board

That final -en is functioning like English the here.

Lägg is the imperative form of lägga.

• lägga = to lay / put / place
• lägg! = put! / place!

So the sentence is giving an instruction or command.

This form does not change depending on who you are speaking to. Swedish does not have different imperative forms like some languages do.

Lägga is commonly used when you put something down onto a surface.

So Lägg spelpjäsen på spelplanen sounds natural for placing a game piece on a board.

A rough comparison:

• lägga = lay/put something down
• sätta = set/place, often upright or into position
• placera = place/position, more formal or neutral

In everyday instructions for a board game, lägg is a very natural choice.

På usually means on.

Here it tells you where the piece should go:

• på spelplanen = on the game board

That is the normal preposition because a board is thought of as a surface.

Swedish often uses på both for being on something and moving something onto it, so the same preposition works well here.

This is standard Swedish word order for an imperative sentence:

• Lägg = verb
• spelpjäsen = direct object
• på spelplanen = prepositional phrase showing location

So the pattern is basically:

Verb + thing + place

That is exactly what you would expect in a simple instruction like this.

Because both nouns are common gender nouns, and in the singular definite form, common gender nouns usually take -en.

Base forms:

• en spelpjäs
• en spelplan

Definite singular:

• spelpjäsen
• spelplanen

So the matching -en ending is not a coincidence; it comes from the same grammar rule.

The dictionary forms are the indefinite singular forms:

• en spelpjäs = a game piece
• en spelplan = a game board

If you want the noun by itself without the article, the bare forms are:

• spelpjäs
• spelplan

Those are the forms you would usually see in a vocabulary list.

The ä sound is similar to the e in English bed, though the exact Swedish sound is a bit different.

So lägg sounds roughly like legg, but with a short Swedish vowel and a stronger final gg sound.

A rough pronunciation of the whole sentence could be written:

legg SPAYL-pyess-en paw SPAYL-plan-en

That is only approximate, but it helps as a starting point.

Yes, but it would change the meaning.

• Lägg spelpjäsen på spelplanen = Put the game piece on the game board.
• Lägg en spelpjäs på en spelplan = Put a game piece on a game board.

So the original sentence sounds like the speaker is referring to a specific piece and a specific board, probably already known from the situation.

Yes. It sounds like a normal instruction, especially in contexts such as:

• board game rules
• classroom instructions
• telling someone how to set something up

It is short, direct, and idiomatic Swedish.