On peut s’asseoir sur le banc.

In this sentence, on means something like one, people, or we, depending on context.

So On peut s’asseoir sur le banc can mean:

• One can sit on the bench
• People can sit on the bench
• We can sit on the bench

In everyday French, on is very commonly used instead of nous for we in spoken language.

Because the subject is on, and on takes third-person singular verb forms.

So:

• on peut = one/we can
• nous pouvons = we can

Even when on means we, the verb still stays singular:

• On peut partir = We can leave

The apostrophe appears because se becomes s’ before a vowel sound.

The full verb is s’asseoir = to sit down / to sit oneself down.

Compare:

• se lever
• s’asseoir

This is called elision:

• se + asseoir → s’asseoir

French often uses reflexive verbs where English does not.

S’asseoir literally has the idea of to seat oneself, but in normal English we usually just say to sit down or to sit.

So in French, the reflexive form is standard:

• Je m’assois
• Tu t’assois
• On peut s’asseoir

Even though it looks more complicated than English, it is just the normal way to express this action in French.

After a conjugated modal verb like pouvoir (can / to be able to), French uses an infinitive.

So:

• On peut s’asseoir
• literally: One/We can sit down

This is the same pattern as in English:

• can sit

And in French:

• peut = conjugated verb
• s’asseoir = infinitive

Sur usually means on.

So:

• sur le banc = on the bench

It shows position or contact with a surface.

Examples:

• sur la table = on the table
• sur la chaise = on the chair
• sur le banc = on the bench

Banc is a masculine noun in French, so it takes le in the singular.

• le banc = the bench
• un banc = a bench

If it were plural:

• les bancs = the benches

So the article agrees with the noun’s grammatical gender and number.

Banc is pronounced roughly like bahn with a nasal vowel.

A few useful points:

• The final c is normally not pronounced
• The an is nasal
• It does not sound like English bank

So banc and banque are different:

• banc = bench
• banque = bank

Yes.

• s’asseoir means to sit down
• s’asseoir sur quelque chose means to sit on something

So in this sentence:

• s’asseoir sur le banc = to sit on the bench

Without the second part, the sentence would just say that sitting down is possible, without saying where.

Yes. Pouvoir can express both:

• ability = can / be able to
• permission = may / be allowed to

So On peut s’asseoir sur le banc could mean:

• We can sit on the bench because it is possible
• We may sit on the bench because it is allowed

The exact meaning depends on context.

Yes, depending on style and meaning.

Some alternatives:

• Nous pouvons nous asseoir sur le banc.
  More formal or explicit we can sit on the bench
• On peut s’installer sur le banc.
  More like we can settle onto the bench
• On peut s’asseoir là, sur le banc.
  Adds emphasis: We can sit there, on the bench

The version with on is very natural in everyday French.