Wir decken eine Karte vom Ablagestapel auf.

Because the verb here is the separable verb aufdecken.

In a normal main clause in German:

• the conjugated part goes in position 2: decken
• the separable prefix goes to the end: auf

So:

• Wir decken ... auf.

The full dictionary form is aufdecken, but in this sentence it gets split.

Aufdecken means something like:

• to uncover
• to reveal
• in a card game, often to turn face up or to flip over

That is different from decken, which by itself usually means things like:

• to cover
• to set the table
• to provide for / to cover a cost

So aufdecken is not just the ordinary verb decken plus a random auf. It is its own verb with its own meaning.

Eine Karte is in the accusative case because it is the direct object of the verb aufdecken.

We are turning over what? → eine Karte

For the feminine noun die Karte, the indefinite article is:

• nominative: eine
• accusative: eine

So the form looks the same in both cases, but here its function is accusative.

Vom is a contraction of:

• von dem → vom

The preposition von always takes the dative case, so:

• der Ablagestapel
• von dem Ablagestapel
• contracted: vom Ablagestapel

So vom Ablagestapel literally means from the discard pile.

German often uses von when something comes off a surface, pile, or source point.

A discard pile is thought of as a stack/pile, not a container you reach into. So:

• vom Ablagestapel = from the discard pile / off the discard pile

By contrast, aus is more natural for something coming out of an enclosed space, such as:

• aus der Tasche = out of the bag
• aus der Schachtel = out of the box

So von fits the image of taking a card from a pile.

It is a compound noun:

• Ablage = something like depositing, putting aside, or in game context discard area
• Stapel = stack or pile

So Ablagestapel is literally a discard stack/pile.

Like many German compound nouns, the last part determines the grammatical gender. Since der Stapel is masculine, the whole word is masculine:

• der Ablagestapel

That is why we get:

• dem Ablagestapel
• vom Ablagestapel

That is standard German main-clause word order with a separable verb.

Pattern:

• subject
• conjugated verb
• other sentence elements
• separable prefix at the end

So:

• Wir = subject
• decken = conjugated verb
• eine Karte = direct object
• vom Ablagestapel = prepositional phrase
• auf = separable prefix

German usually keeps the object and other complements together before the final prefix.

Yes. German present tense often covers both:

• simple present: We turn over a card
• present progressive: We are turning over a card

The exact English translation depends on context.

In instructions or game rules, German often uses the present tense where English also might say:

• We turn over a card from the discard pile

In live narration, it could also be:

• We’re turning over a card from the discard pile

Yes. In rules, demonstrations, and explanations, German often uses wir in a friendly, inclusive way, similar to English we in:

• Now we draw a card
• Then we place it here

It does not always mean that the speaker is literally playing too. It can simply guide the listener through the steps.

So Wir decken eine Karte vom Ablagestapel auf can sound natural in explanations such as rules, tutorials, or spoken instructions.