These and Those

Generally, English, unlike other languages, does not change its adjectives to match singular or plural forms.

a good book
good books
a delicious meal
several delicious meals

Note how good, delicious, etc. are the same for singular and plural nouns.

However, there is a class of words called determiners which are similar in some ways to adjectives.  Some of these do change.  Here's an important example, which in my experience many Polish student of English are unaware of.

I like this book.    I like these books.

I don't know that man.   I don't know those men.

The plural form of this is these.  The word these rhymes with sneeze and please. 

We use this with countable singular and uncountable nouns, such as this money, this tree, this information, this milk, this television set, this stupid reality show.

We use these with countable plural nouns, such as these trees, these bananas, these crazy students, these days, these films, these drunken football hooligans, etc.

The rule is similar with that and those.  The word those rhymes with froze and chose.

I'm in love with that girl.   I'm in love with those girls.

I can't stand that idiot.   I can't stand those idiots.

Notice that we use this and these to identify things which are nearby, or are under consideration at the moment, while we use that and those to identify things which are more distant, or which we have already discussed and rejected, or which we view unfavourably.

I think you should take this one (here) and leave that one (there).

We shouldn't waste any more time on that solution.  This one is much more logical.