This is what you need:
garden cress seeds
a flat container
paper kitchen roll
Take a piece of paper kitchen roll and fold it to the size of your container. Place it inside the container, laying it flat on the bottom.
Now place the seeds on the folded paper.
Add water until the seeds are covered for about 1/4 of an inch with water.
The seeds will float on the water as you can see below.
Now place the container in a quiet sunny place. I usually leave it outside the kitchen windown sill.
Now leave the seeds to get some sun make sure to check back on your garden cress tomorrow to check if you have to add water (always keep the container wet) and to see how fast your garden cress will be growing.
Only 24 hourse later your garden cress has already started to grow:
After 4-5 days your garden cress is ready for a first harvest. Cut off as much as you need and keep the remaining cress in the container making sure they have enough water for future consumption. The brown spots are the shells of the seed, just brush them off.
By the way, growing water cress works just the same way, but it does take a longer, you will need weeks before being able to harvest.
The picture below shows water cress after 2 weeks.