Countries and Nationalities.
Talking about people and things from a country, you have to know
a) The adjective used to refer to the country, its culture, products,...
Greek sculpture, Danish industry, French champagne, Spanish folklore.
b) The noun for a person from the country
A Frenchman, a Portuguese, a Dane, a Spaniard.
c) Referring to the whole nation.
The Greeks, the Danes, the French, the Japanese.
We'll only write some irregular examples.
Country Adjective Person Nation
Denmark Danish a Dane the Danes
Sweden Swedish a Swede the Swedes
Poland Polish a Pole the Poles
Turkey Turkish a Turk the Turks
Scotland Scottish a Scot the Scots.
Spain Spanish a Spaniard the Spanish
Wales Welsh a Welshman the Welsh
Ireland Irish an Irishman the Irish
The words ending in -man have feminine forms in -woman and plurals in -men and -women. There is no difference in pronunciation between the singular and plural.
The Scots prefer the adjective Scottish, but other people often use the word Scotch (you should not use it). The whisky is always called Scotch. A Scot can also be called a Scotsman.
No -s on the plural:
the Chinese, the Portuguese, the Japanese, the French, the Spanish, the Welsh, the Irish...