Their house is red. Their house is red.
Adjectives describe nouns.
=====Construction=====
1. Before a noun: It's a blue car.
2. After 'to be': The car is/isn't blue.
There isn't a plural form:
The cars are reds. 
The cars are red. 
=====Uses=====
Adjectives give information about people and things. For example: colour, size and nationality.
It's green.
It's a big city.
They're French.
The river is 100km long.
Mont Blanc is 4,810m high.
She's 1.75m tall.
=====Examples=====
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| There are two purple sofas and a pink chair.
| Is your office big or small? |
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| My boss is American and his clients are Japanese. | James is tall. |
King Charles is British.
We use adjectives for nationality before a noun or after 'to be'. They always begin with a capital letter.
I work with a Spanish man.
We have a Swedish manager.
He's French.
They're German.
We use adjectives ending in 'an' as nouns:
He's a German/an American/an Italian.
He's a Swedish/a French/a Japanese.
For the nouns of nationalities ending with -ese, -ish, or -ch, we can use 'the' to talk about the whole population.
The English often take their holidays in France.
For nationalities ending with -n, generally no article is necessary.
Americans are friendly.
Here are some examples with their countries:
Ending | Country | Nationality | Nouns |
'an' | Angola Australia Belgium Canada Egypt Germany India Italy Korea Latvia Mexico Norway Peru USA | Angolan Australian Belgian Canadian Egyptian German Indian Italian Korean Latvian Mexican Norwegian Peruvian American
| an Angolan (person) an Australian (person) a Belgian (person) a Canadian (person) an Egyptian (person) a German (person) an Indian (person) an Italian (person) a Korean (person) a Latvian (person) a Mexican (person) a Norwegian (person) a Peruvian (person) an American (person)
|
'ish' | Denmark England Finland Poland Scotland Spain Sweden UK
| Danish English Finnish Polish Scottish Spanish Swedish British | a Danish person; a Dane an English person; an Englishman [not 'Englishwoman'] a Finnish person; a Finn a Polish person; a Pole a Scottish person; a Scot a Spanish person; a Spaniard a Swedish person; a Swede a British person |
'ese' | Burma China Japan Malta Nepal Portugal Senegal Vietnam | Burmese Chinese Japanese Maltese Nepalese Portuguese Senegalese Vietnamese
| a Burmese person a Chinese person a Japanese person a Maltese person a Nepalese person a Portuguese person a Senegalese person a Vietnamese person |
Other | France Greece Iceland Iraq Pakistan Switzerland Wales | French Greek Icelandic Iraqi Pakistani Swiss Welsh | a French person a Greek person; a Greek an Icelandic person an Iraqi person; an Iraqi a Pakistani person; a Pakistani a Swiss person; a Swiss a Welsh person
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Note that 'person' can also be 'man', 'woman', 'child', 'friend', 'colleague', 'manager' etc.
Examples:
This is the Irish flag. 
I like Italian ice-cream.
Emily is English. Her friend, Karine, is French. Andrew is a Swede. Tomoko is a Japanese visitor.
