English has a strict habit: almost every sentence needs a subject, even when there is no real 'doer'. To introduce the fact that something exists, English uses 'there': 'There is a problem.' To talk about weather, time, and things already known, it uses 'it': 'It is raining', 'It is five o'clock.' If you mix them up and say 'It has a problem in the room', listeners will pause, because that sentence says the room's problem belongs to some mysterious 'it'.

The little words 'one' and 'ones' solve a different everyday problem: repeating nouns. In a shop you do not say 'I like the blue shirt, but the white shirt is cheaper.' You say 'I like the blue one, but the white one is cheaper.' Mastering it, there, one, and ones makes your English smoother in exactly the situations beginners meet most: describing places, shopping, and pointing things out.

Start with 'there is / there are'. Use this pattern to introduce something for the first time — to say that it exists or is present in a place: 'There is a pharmacy on this street', 'There are two messages for you.' Match the verb to the noun that follows: there is + singular (there is a chair), there are + plural (there are four chairs). The negative and question forms are easy: 'There isn't any milk', 'Is there a bank near here?', 'Are there any seats left?'

Now 'it'. Use it to refer back to a thing you have already mentioned or that everyone can see: 'I bought a jacket. It was on sale.' It also fills the subject spot for weather, time, distance, and dates, where no real thing does the action: 'It is cold today', 'It is nearly midnight', 'It is ten kilometers to the airport.' In these sentences, it does not point to anything — it just keeps the subject seat warm.

Here is the clean division of labor. First mention, new information: there. Second mention, known information: it. Watch them work together: 'There is a cafe on the corner, and it opens at seven.' There introduces the cafe; it refers back to it. Saying 'It is a cafe on the corner' as an opener sounds wrong because the listener does not yet know what 'it' means.

Next, 'one' and 'ones'. These replace a countable noun you have just said, so you do not repeat it. Singular: 'My phone is old, so I need a new one' (one = phone). Plural: 'These shoes hurt; the black ones are more comfortable' (ones = shoes). You usually put an adjective or 'this/that/which' in front: the red one, a bigger one, that one, which ones? Remember that one/ones only replaces countable nouns — for uncountable nouns like money, water, or advice, use 'some' instead: 'I need some.'

A final contrast to remember. 'There is one' answers how many: 'Is there a printer? Yes, there is one on the desk.' 'It is the one' identifies which: 'It is the one near the window.' There counts and introduces; it and one point and choose.

1. 1. There is a small park behind our building.

   First mention of the park, so there is introduces it.

2. 2. There are three new emails in your inbox.

   The noun emails is plural, so the verb becomes are.

3. 3. I tried the soup, and it was too salty.

   It points back to the soup, already mentioned.

4. 4. It is windy today, so take a warm coat.

   It fills the subject spot for weather; nothing real does the action.

5. 5. Is there a pharmacy open near the station?

   To ask if something exists, start the question with is there.

6. 6. There isn't any sugar left for the cake.

   The negative of there is uses isn't plus any.

7. 7. My old laptop died, so I ordered a new one.

   One replaces laptop, so the noun is not repeated.

8. 8. I like these cups, especially the blue ones.

   Ones replaces the plural noun cups after the adjective blue.

9. 9. It takes twenty minutes to walk to the market.

   For time and distance, it is the empty subject.

10. 10. There was an accident on the highway this morning.

    In the past, there was introduces a singular event.

11. 11. Which one is yours, the green bag or the gray one?

    One helps you choose between two known bags.

12. 12. There are no tickets left, so we will go tomorrow.

    There are no + plural noun is a common negative pattern.

13. 13. The rooms are similar, but the corner one has more light.

    One stands in for room after the describing words corner.

14. 14. Is it far from here? No, it is very close.

    It carries the idea of distance in both question and answer.

The central mistake is using 'it has' or 'it is' to introduce something new, like the error 'It has a problem in the room.' Wrong: 'It has a problem in the room.' Right: 'There is a problem in the room.' When you announce that something exists, English wants there, not it. Use it only after the thing is already known: 'There is a problem, and it is serious.'

A second mistake is forgetting to match the verb after there: 'There is many people at the party', 'There are a message for you.' Wrong: 'There is many people.' Right: 'There are many people.' Look at the noun right after the verb — singular takes is/was, plural takes are/were. This small check keeps the pattern correct in every tense.

A third mistake is repeating the noun instead of using one or ones, or dropping the word completely: 'I want the red' or 'I want the red shirt, not the blue shirt.' Wrong: 'I want the red.' Right: 'I want the red one.' After an adjective like red, big, or cheap, English needs one (singular) or ones (plural) to stand in for the countable noun. But do not use one for uncountable nouns — for coffee or money, say 'some': 'I'd like some.'

• Introducing something new? Start with there is or there are, never 'it has'.
• There is + singular, there are + plural — check the noun after the verb.
• Use it for things already mentioned, and for weather, time, and distance.
• Pair them: 'There is a cafe, and it opens early.'
• After an adjective, add one or ones: the red one, the cheap ones.
• One and ones replace countable nouns only; for uncountables, use some.