Study the information about few, a few, little, a little, fewer, less.
1. We can use few and a few with plural countable nouns.

Few onions, a few onions
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We should use little, a little with uncountable nouns.

I have little time to do it.
2. Few and little are negative, they use in the meaning ‘hardly any’.

I have got few friends.
3. A few and a little can be used when we mean something positive.

I have a few apples to eat.

You can use  ‘only’ with a few and a little.

I have got only a few relatives.
Fewer and less.
1. Fewer is the comparative of few. Less is the comparative of little.
2. Fewer goes with plural countables.

Fewer videos have been imported his year than last.

3. Less goes with uncountables.

Less oil has been produced this year than last.

4. Informally, we often use less with uncountables. Some native speakers think it’s wrong.

Less people are travelling abroad this year.
L.G Alexander. Longman English Grammar practice for intermediate students- Harlow: Longman, 296p.