In terms of producing energy there are a few different ways of doing this. Most witches will have a favoured method of raising energy. This can be a purely mental process or can involve physical elements such as dance or Yoga. One of the best ways I ever heard was to use a hula hoop to draw up the energy from the earth. If I ever master the art of hooping I would so pinch that idea!
The idea behind the raising of energy isn’t dissimilar to the idea of potential energy in science. Think the pulling back of an elastic band which gets more and more energy “stored” as the tension is tightened. When it finally pings it zips across the room using all that potential energy that has been raised through the process of tightening the tension on the band. The witch uses herself as an energy store in the same way, she learns how to gather energy, either raising it from the earth or centering her own energy and power into a focus and then she directs her intent forward using that energy for maximum effect.
Naturally the better you are at finding and focusing that energy the more powerful the force you are able to release. This is why it is important to play with different techniques and what works for you in order to be able to project your intent to your own full potential.
You ask about meditation in your question and how to use it to relax yourself. I think the most important thing about meditation is finding a visualisation that works for you. The common misconception that making your mind blank is the way forward is flawed as very, very few people are skilled enough to have the ability to think of nothing at all. I believe the best way to start with meditation is to focus on a single colour and only allow objects and concepts associated with that colour to enter your mind. This will help you learn how to block unnecessary thoughts from your mind and also to control your own mental processes. Focusing on earth colours like green and blue will also induce a sense of calm. I’d also suggest you have some way of ensuring you are not going to be interrupted (I have a sign on my door and when it is turned over everybody in the household knows not to interrupt under any circumstances), no distractions like mobile phones or computers, as much natural light as possible (outdoor light or candles), gentle music without lyrics and a subtle scent in the air. Don’t make the mistake of filling the room so full of incense that you choke throughout your meditation. The idea behind this is that all your senses are being lulled into calm making it easier for you to focus on the images you wish to hold in your mind.
Have a read of this question too How do I switch off my mind when I meditate?