Der Topflappen liegt neben dem Herd, weil die Form aus dem Ofen noch heiß ist.

Because the nouns have different grammatical genders and cases here.

• Topflappen is masculine, and it is the subject of the main clause, so it is in the nominative:
  • der Topflappen
• Herd is also masculine, but after neben in this sentence it is in the dative:
  • dem Herd

So:

• nominative masculine: der
• dative masculine: dem

That gives you:

• Der Topflappen liegt ...
• ... neben dem Herd

Because neben is a two-way preposition. That means it can take either:

• dative when talking about location: where something is
• accusative when talking about direction/movement: where something is going

Here, the sentence describes a location:

• The potholder is lying next to the stove

So German uses the dative:

• neben dem Herd

If there were movement toward that place, you would use the accusative:

• Ich lege den Topflappen neben den Herd.
  • I put the potholder next to the stove.

A useful contrast:

• liegt neben dem Herd = is next to the stove
• lege neben den Herd = put next to the stove

German often prefers specific verbs for position, where English often just says is.

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

A Topflappen is treated as something lying flat, so:

• Der Topflappen liegt ...

This sounds more natural than:

• Der Topflappen ist neben dem Herd.

That version is not impossible, but it is less idiomatic if you are describing physical position.

Because weil introduces a subordinate clause, and in German subordinate clauses the conjugated verb usually goes to the end.

Main clause:

• Der Topflappen liegt neben dem Herd

Subordinate clause with weil:

• weil die Form aus dem Ofen noch heiß ist

Notice that ist comes last.

This is one of the most important German word-order rules:

• main clause: conjugated verb usually in second position
• subordinate clause: conjugated verb usually at the end

Compare:

• Die Form ist noch heiß.
• ..., weil die Form noch heiß ist.

Here noch means still.

So:

• noch heiß = still hot

It suggests that the baking dish has come out of the oven and has not cooled down yet.

That is a very common use of noch:

• Ich bin noch müde. = I’m still tired.
• Ist das Essen noch warm? = Is the food still warm?

In this context, die Form does not mean abstract shape/form. It usually means a dish, tin, mold, or baking pan, depending on context.

Because the sentence also mentions aus dem Ofen, learners would usually understand die Form here as something like:

• a baking dish
• a casserole dish
• a baking tin/pan

German often uses Form for containers used in baking or cooking, such as:

• Backform = baking tin/pan
• Auflaufform = casserole dish

So die Form here is probably some oven-safe container.

Because aus takes the dative case.

• Ofen is masculine
• dative masculine article = dem

So:

• aus dem Ofen = out of the oven / from the oven

This is a fixed rule:

• aus + dative

Examples:

• aus dem Haus
• aus der Küche
• aus den Schubladen

This is a very common question because English uses stove, oven, and sometimes cooker differently.

In German:

• der Herd usually means the stove/cooker unit, often the whole appliance
• der Ofen means the oven or sometimes a heating oven/stove depending on context

In this sentence:

• neben dem Herd = next to the stove/cooker
• aus dem Ofen = out of the oven

So the potholder is next to the stove because the dish from the oven is still hot.

In everyday German, Herd can sometimes refer to the whole kitchen appliance that includes the oven.

Because in German, a subordinate clause introduced by weil is separated from the main clause by a comma.

So this is standard punctuation:

• Der Topflappen liegt neben dem Herd, weil die Form aus dem Ofen noch heiß ist.

This is not optional in standard German writing.

Because heiß is used here as a predicate adjective, not directly before a noun.

Compare:

1. Predicate adjective — no ending

   • Die Form ist heiß.

2. Attributive adjective — adjective ending required

   • die heiße Form

In your sentence, the structure is:

• die Form ... ist heiß

So heiß stays in its basic form.

Yes, but the grammar and tone change slightly.

1. weil

Very common for because.

• Der Topflappen liegt neben dem Herd, weil die Form aus dem Ofen noch heiß ist.

Verb goes to the end in the subordinate clause.

2. denn

Also means because, but it introduces a main clause, so normal word order stays.

• Der Topflappen liegt neben dem Herd, denn die Form aus dem Ofen ist noch heiß.

This sounds a bit more formal or written than weil in many situations.

3. da

Can also mean since/because, often when the reason is seen as known or obvious.

• Der Topflappen liegt neben dem Herd, da die Form aus dem Ofen noch heiß ist.

This can sound a bit more formal or literary.

For everyday spoken German, weil is usually the safest choice.

Because that is the thing being described as still hot.

In the clause:

• weil die Form aus dem Ofen noch heiß ist

the subject is:

• die Form aus dem Ofen

and the predicate is:

• noch heiß ist

You can think of aus dem Ofen as extra information attached to die Form:

• the dish from the oven

So the full idea is:

• because the dish from the oven is still hot

Yes. German allows some flexibility.

For example, you could start with the weil clause:

• Weil die Form aus dem Ofen noch heiß ist, liegt der Topflappen neben dem Herd.

That is still completely correct.
Notice what happens in the main clause after the subordinate clause:

• liegt comes before der Topflappen

That is because the entire weil clause takes the first position, so the verb in the main clause must still be in second position.

This is a very important German pattern:

• Weil ..., liegt der Topflappen ...

not

• Weil ..., der Topflappen liegt ... ❌