I have a planted tank with some plants that booming. Now from what i have heard when you trim the plants you can take the trimmings and plant them creating other plants. Is this true?
Depends on the type of plant. Some plants, mostly stems can be trimmed and replanted. Other plants, swords, vals and crypts, put out runners from which new plants grow. Some develop bulbs.
Stem plants will usually grow when clippings are stuck in the substrate, the lower portion will fork, creating 2 new stems where it was cut (so cut fairly low).
List your plants and it will be easier to give specific suggestions. In most cases the aforementioned techniques work, but some plants differ in sensitivities and requirements.
On stem plants yes as several people have said. Cut them a 1/4" - 1/2" below the node, pull the leaves off the node, replant. Roots will grow from the node.
What types of plants do you have? This will help us to better assist you.