Wir schmieren das Fahrradschloss.

Here, schmieren means something like to grease, to oil, or to lubricate.

Its basic idea is applying a greasy or oily substance to something. In other contexts, it can also mean to smear or to spread something on a surface, so the exact English translation depends on what is being treated.

With das Fahrradschloss, the natural meaning is that we are lubricating the bicycle lock.

Because schmieren is the infinitive form of the verb, and in the sentence it has been conjugated for wir.

The verb is conjugated like this in the present tense:

• ich schmiere
• du schmierst
• er / sie / es schmiert
• wir schmieren
• ihr schmiert
• sie / Sie schmieren

So wir schmieren means we grease / we are greasing.

Because it is the direct object of the verb schmieren.

The verb schmieren usually takes an object: you grease something. In this sentence, the thing being greased is das Fahrradschloss.

Since Fahrradschloss is a neuter noun, its definite article is:

• das in the nominative
• das in the accusative

So the object appears as das Fahrradschloss.

Because the noun Schloss is neuter, and the compound noun takes its gender from the last element.

• das Schloss = the lock / the castle
• das Fahrradschloss = the bicycle lock

In German compound nouns, the final part is the main noun and determines the gender. Since Schloss is neuter, Fahrradschloss is also neuter, so you say das Fahrradschloss.

It is made of:

• das Fahrrad = bicycle
• das Schloss = lock

Together, das Fahrradschloss literally means bicycle-lock, or more naturally, bicycle lock.

This is very common in German: instead of using separate words like in English, German often combines them into one noun.

German main clauses normally follow the verb-second rule.

In Wir schmieren das Fahrradschloss:

1. Wir = first element
2. schmieren = verb in second position
3. das Fahrradschloss = the rest of the sentence

This is standard German word order for a simple statement.

Yes. The German present tense often covers both:

• We grease the bicycle lock
• We are greasing the bicycle lock

German does not need a separate form like English are greasing in order to express an action happening now. The simple present can do that.

Yes. Das Schloss can mean either:

• lock
• castle / palace

The meaning depends on context.

In das Fahrradschloss, it clearly means lock, because a bicycle castle would make no sense.

Yes, that is also possible.

• ölen = to oil
• schmieren = to grease / lubricate / smear

In practice, both can work depending on context. schmieren is a bit broader and often suggests applying grease or lubricant. ölen specifically suggests oiling something.

So Wir schmieren das Fahrradschloss and Wir ölen das Fahrradschloss can both be natural, though they are not always exactly identical in nuance.

Because in German, all nouns are capitalized.

So in this sentence:

• Wir is capitalized because it is the first word of the sentence.
• Fahrradschloss is capitalized because it is a noun.

This is a general rule in German and is very important for correct writing.