You need:

White PVA glue

Water

Food colouring

Borax
Method:

Mix 1 tablespoon of white PVA glue, one tablespoon of
water, and one drop of food colouring into a container.

In a second container dissolve one teaspoon of Borax
into one tablespoon of warm water.

Mix the glue and borax mixture together.

The slime should form instantly. Lift it out of container
and throw out the left over liquid.