Die Ereigniskarte liegt in der Kartenauslage.

German often uses position/location verbs where English just uses is.

• liegen = to lie, to be lying, to be located
• stehen = to stand
• sitzen = to sit

A card is thought of as something that lies somewhere, so Die Ereigniskarte liegt ... is the natural choice.

Using ist would usually sound less specific or less idiomatic here.

It is nominative singular because it is the subject of the sentence — the thing doing the verb.

• die Ereigniskarte = the event card
• liegt = lies / is located

So the sentence structure is:

• Die Ereigniskarte = subject
• liegt = verb
• in der Kartenauslage = location

Because in is a two-way preposition in German.

• dative after in = location, no movement
• accusative after in = movement into something

Here, the card is already there, so this is a location idea:

• Die Ereigniskarte liegt in der Kartenauslage.

If the sentence described movement into that area, you would use accusative:

• Die Ereigniskarte kommt in die Kartenauslage.

Because der here is the dative feminine form of die.

For feminine nouns:

• nominative: die
• accusative: die
• dative: der
• genitive: der

So:

• die Kartenauslage = nominative
• in der Kartenauslage = dative, because it follows in in a location meaning

So der does not mean the noun is masculine here.

They are both compound nouns, and in German, the last part of a compound determines the gender.

• Ereigniskarte = Ereignis

  • Karte
  • last part: Karte
  • Karte is feminine
  • so die Ereigniskarte

• Kartenauslage = Karten

  • Auslage
  • last part: Auslage
  • Auslage is feminine
  • so die Kartenauslage

This is a very useful rule for German compounds.

A compound noun is a noun made by joining smaller words together.

Here:

• Ereigniskarte

  • Ereignis = event
  • Karte = card
  • so: event card

• Kartenauslage

  • Karten = cards
  • Auslage = display, layout, area where things are laid out
  • so: something like card display area or card layout area

German uses compounds all the time, especially in games, instructions, and technical language.

That -n- comes from Karten, which is the plural form of Karte.

So the compound is built like this:

• Karten
  • Auslage = Kartenauslage

In German compounds, the first part is often not the plain dictionary singular form. It may appear as:

• a plural form
• a stem form
• a linking form

So you should not be surprised if the first part changes a little inside a compound.

Because standard German main clauses usually follow the verb-second rule.

In this sentence:

• Die Ereigniskarte = position 1
• liegt = position 2
• in der Kartenauslage = the rest

That gives:

• Die Ereigniskarte liegt in der Kartenauslage.

You can move another element to the front, but the verb still stays second:

• In der Kartenauslage liegt die Ereigniskarte.

Both are correct, but the second version gives more emphasis to the location.

Because in German, all nouns are capitalized, not just proper names.

So in this sentence:

• Ereigniskarte is capitalized because it is a noun
• Kartenauslage is capitalized because it is a noun

But words like liegt, in, and der are not nouns, so they are not capitalized.

Because the subject is singular:

• die Ereigniskarte = one event card

The verb liegen is conjugated to match the subject:

• ich liege
• du liegst
• er/sie/es liegt
• wir liegen
• ihr liegt
• sie/Sie liegen

Since Ereigniskarte is singular and feminine, it takes the same verb form as sie:

• Die Ereigniskarte liegt.

Yes, sometimes, but it changes the style.

• Die Ereigniskarte liegt in der Kartenauslage.
  More natural and concrete for a physical object like a card.

• Die Ereigniskarte befindet sich in der Kartenauslage.
  More formal, more neutral, and a bit less vivid.

For game instructions or descriptions of where pieces/cards are, liegt is often the most natural choice.