De bij is klein.

In Dutch, singular nouns usually take either de or het. Bij is a de-word, so you say de bij.

Unfortunately, there is not always a simple rule you can rely on, so for many nouns you just learn the article together with the word:

• de bij = the bee
• het huis = the house

A useful tip: the plural article is always de, so:

• de bij
• de bijen = the bees

Bij is pronounced roughly like English buy.

A few details:

• b sounds like English b
• ij is a Dutch vowel sound that is often close to English eye in many learning materials
• So bij sounds approximately like b-eye

Also, ij is a very common Dutch spelling, so it is worth getting used to early.

Because klein comes after the verb is here, it is a predicate adjective. In Dutch, predicate adjectives usually do not take -e.

So:

• De bij is klein. = The bee is small.

But when the adjective comes before the noun, it usually does take -e:

• de kleine bij = the small bee

This is a very common difference in Dutch:

• Het huis is groot.
• het grote huis

Is is the third-person singular form of the verb zijn, which means to be.

So:

• ik ben = I am
• jij bent = you are
• hij/zij/het is = he/she/it is

In De bij is klein, de bij is singular, so Dutch uses is.

Yes. This is a very standard Dutch main-clause pattern:

subject + verb + complement

So here:

• De bij = subject
• is = verb
• klein = adjective/complement

This is exactly the kind of simple sentence structure beginners see a lot in Dutch.

For a yes/no question, Dutch usually puts the verb first:

• Is de bij klein? = Is the bee small?

No. Bij can also be a very common preposition meaning things like at, with, or near, depending on context.

For example:

• Ik ben bij mijn vriend. = I am at my friend’s place / with my friend.

But in De bij is klein, it clearly means bee, because:

• it has the article de
• it is being used as a noun

So Dutch learners should know that bij can be both a noun and a preposition.

Because Dutch does not capitalize all nouns the way German does.

In this sentence, only De is capitalized because it is the first word of the sentence.

So:

• De bij is klein.
• Ik zie de bij.

In both cases, bij stays lowercase unless there is some special reason to capitalize it.

The plural of bij is bijen, and the verb changes too:

• De bij is klein. = The bee is small.
• De bijen zijn klein. = The bees are small.

Notice the changes:

• bij → bijen
• is → zijn

The adjective klein stays the same here because it is still a predicate adjective after the verb.

Yes, grammatically you can. But it changes the meaning slightly.

• De bij is klein. = The bee is small.
  This usually refers to a specific bee, or to the bee as a known thing.

• Een bij is klein. = A bee is small.
  This sounds more general or indefinite.

So both are possible, but de and een do different jobs:

• de = the
• een = a/an

Klein is a regular adjective meaning small.

It can be used:

• after a verb: De bij is klein.
• before a noun: de kleine bij

It can also be compared:

• klein = small
• kleiner = smaller
• kleinst = smallest

So you could also say:

• De bij is kleiner. = The bee is smaller.
• De kleinste bij = The smallest bee

It is perfectly grammatical and natural, but it does sound a bit like a simple beginner sentence because it is so short and straightforward.

That is not a bad thing. Sentences like this are very useful because they clearly show:

• the article: de
• the noun: bij
• the verb: is
• the adjective: klein

So while a native speaker would understand it immediately, in real conversation you would often get more context, such as:

• Die bij is klein. = That bee is small.
• De bij is heel klein. = The bee is very small.