Three types of er

There are three main uses of the word er: locative, existential, and quantitive. The first two uses are related, and derived from the adverb of place daar.

Locative er

Locative er is the unstressed form of the adverb daar (‘there’) and is often used when the same location is referred to for a second time in the same conversation. Daar and (locative) er are adverbs of place, indicating a location, hence the term locative.

Daar staat de ketjap en de sambal staat er ook.
There is the ketjap and the sambal is there too.

Ik ga naar de bibliotheek om te studeren. Ook ontmoet ik er mijn vrienden.
I go to the library to study. I also meet my friends there.

Note that it is possible to use daar in the above examples instead of er (e.g. Daar staat de ketjap en de sambal staat daar ook), but this only happens if it needs emphasis.

Locative er is usually put after the subject and finite verb cluster in a main clause.

Rotterdam is een leuke stad. Ik kom er altijd graag.
Rotterdam is a nice city. I always like to go there.

Rotterdam is een leuke stad. Zaterdag ga ik er weer naartoe.
Rotterdam is a nice city. I will go there again on Saturday.

Existential er

Existential er is derived from the locative meaning, but with this type of er there is no parallel stressed form as there is with locative er. Note that not only the verb zijn can be used in combination with existential er, but also verbs of position and even more general verbs:

Er zijn wel 30.000 studenten in Sheffield.
There are at least 10,000 students in Sheffield.

Wie is er nu weer zoek?
Who has got lost now?

Er staat een kratje bier in het boodschappenwagentje.
There is a crate of beer in the shopping trolley.

Hoeveel uitwisselingsstudenten studeren er in Rotterdam?
How many exchange students study in Rotterdam?

Make sure that the form of the verb matches the actual subject of the sentence. In the first example above 10.000 studenten is obviously plural, hence the plural form of the verb.

Quantitive er

This type of er is not related to the locative or existential types. Quantitative er occurs invariably with numerals or other words expressing quantities (e.g. één, geen or veel). This er is never translated in English.

Ik heb geen auto, maar mijn zus heeft er wel één.
I do not have a car, but my sister does (have one).

Mag ik een boterham van jou? Ik heb er geen meer.
Can I have one of your slices of bread? I haven’t got any left.

Hier, neem maar een appel van mij, ik heb er toch veel.
Here, have one of my apples, I have many anyway.

It is possible to have quantitative er together in one sentence with a different form of er, as in the first line of a well-known Dutch birthday song:

Er is er één jarig hoera hoera …

In this sentence, the first er is existential, the second quantitative.