पार्सल और लिफ़ाफ़ा काउंटर पर हैं।

Because the subject is compound: पार्सल और लिफ़ाफ़ा = the parcel and the envelope.
Even though each noun is singular by itself, together they make a plural subject, so Hindi uses हैं (are) rather than है (is).

• पार्सल ... है = The parcel is ...
• लिफ़ाफ़ा ... है = The envelope is ...
• पार्सल और लिफ़ाफ़ा ... हैं = The parcel and the envelope are ...

Hindi usually does not use articles like a, an, and the the way English does.
So पार्सल can mean a parcel or the parcel, and लिफ़ाफ़ा can mean an envelope or the envelope, depending on context.

That means the sentence can be understood as something like:

• The parcel and the envelope are on the counter
• or A parcel and an envelope are on the counter

The exact choice comes from the situation, not from separate article words.

Hindi uses postpositions, not prepositions.

In English, you say:

• on the counter

where on comes before the noun.

In Hindi, the equivalent word comes after the noun:

• काउंटर पर = on the counter

So पर is a postposition meaning on / at / upon, depending on context.

और means and. It connects the two nouns:

• पार्सल और लिफ़ाफ़ा = parcel and envelope

It works much like English and.

Because the sentence is talking about one parcel and one envelope.
Each noun is singular individually:

• पार्सल = parcel
• लिफ़ाफ़ा = envelope

The subject becomes plural only because the two singular nouns are joined by और.

So this is like English:

• the parcel and the envelope

not

• the parcels and the envelopes

लिफ़ाफ़ा is masculine.
पार्सल is generally treated as masculine too.

In this sentence, gender does not visibly affect the verb, because the present-tense form हैं shows number here, not gender.

If you added an adjective, gender/number agreement would become more noticeable. For example, an adjective describing both nouns together would normally appear in a masculine plural form.

Hindi normally prefers Subject–Object/Complement–Verb order, so the verb often comes at the end.

Here the structure is:

• पार्सल और लिफ़ाफ़ा = subject
• काउंटर पर = location phrase
• हैं = verb

So the sentence literally follows a pattern like:

• Parcel and envelope counter on are

That is normal Hindi word order.

It is a very common loanword from English, written in Devanagari as काउंटर. Hindi uses many everyday borrowed words, especially for modern objects, places, and institutions.

So this sentence mixes native Hindi grammar with a borrowed noun:

• काउंटर पर = on the counter

That is completely natural.

That dot is called a nuqta. It modifies the consonant to represent a sound that is closer to the English f.

So:

• फ is traditionally more like an aspirated ph
• फ़ is used for f

That is why लिफ़ाफ़ा is pronounced roughly like lifaafaa.

In modern speech, many speakers do not strongly distinguish फ and फ़, but the spelling with फ़ helps show the foreign-style f sound.

Yes. In everyday spoken Hindi, पे is very common and often replaces पर.

So both are possible:

• काउंटर पर हैं — more standard/formal
• काउंटर पे हैं — more conversational

Both mean the same thing here.

Many nouns in Hindi change when they come before a postposition, but some do not show a visible change.
Loanwords like काउंटर often stay the same in form.

So:

• काउंटर
• काउंटर पर

There is no obvious spelling change, even though grammatically it is functioning before a postposition.

In very casual spoken Hindi, people sometimes drop the present-tense to be verb if the meaning is clear. So you might hear:

• पार्सल और लिफ़ाफ़ा काउंटर पर

But in standard, complete Hindi, especially for learners, it is better to keep:

• पार्सल और लिफ़ाफ़ा काउंटर पर हैं।

So yes, omission can happen in speech, but the full sentence with हैं is the safer and more standard form.