Any large jar will do, but preferably for your first attempt, one with a wide top and straight sides for ease of setting up. A large coffee jar or similar is ideal.
Fill your jar with 6-8 inches of good quality potting compost to which you have added a small amount of charcoal. Charcoal keeps the soil fresh and helps with drainage.
Use a funnel to pour your soil through into the jar. The soil should not be too wet as it may stick to the sides of the vessel and look untidy.
To insert the plants into the jar you will need a gadget you can make yourself. Tie or tape old spoons or forks (or one of each) to pieces of thin wood. Make sure your plants are small as this is a delicate operation. Cover the plant roots as well as you can by manipulating the spoons or forks about. Don’t worry too much if you can’t cover all the roots, they will bed themselves in very quickly when they have been watered.
When all the plants are in, water them by dribbling water down the sides of the jar. It is not necessary to water a jar garden as often as a potted plant because with the lid on air cannot circulate and the plants will make their own climate, given the right growing situation. It should only require watering about once a year. The garden will, in effect, be self-watering, as moisture given off by the leaves will condense on the side of the bottle and drip down to water the roots.
Stand your jar garden in a good light, but not direct sunlight or the glass will get too hot