how can we classify meditation based on types and techniques?

While there are many techniques available to us, just as the Buddhist meditation, Japa meditation, Christian meditation and so on, there are basically two major types of meditation that all these techniques are classified in:

• concentrative meditation
• non-concentrative meditation, also called mindfulness meditation (or mindful meditation).

Concentrative meditation

Mostly the Hinduism meditation techniques are concentrative based. In general, concentrative meditation is based on the mind focusing on a specific object or 'thing', such as the breath, a sound, the flame of a candle, a crystal, an image, an idea. By using the mind this way, we help it become more aware overall and gain a clarity that it didn't have before.
Maybe the best known technique of concentrative meditation is to simply sit still while the mind focuses on the breath. This is the technique that beginners to meditation are usually first taught because it is the easiest.
The breath comes from within and it is easier to focus on it than on various sounds that could become annoying, or on a candle which can become distracting.
Also focusing on the breath helps not only with the meditating act but also with simply calming the person, so the beginner meditator can see some benefits of meditation right away. It is much easier to have the excitement and motivation to do something when there are visible benefits that can be felt immediately.

Non-concentrative meditation

The non-concentrative types are also called mindfulness meditation or even zen meditation due to the way it is practiced (see again how types of meditation are used synonymously with meditation techniques?). While the concentrative types are focused more on the sounds, thoughts, ideas, images, etc, here the awareness on these very things becomes detached instead.
You might say that in both cases we focus on the same thing. Not quite so.
In the first, you focus your attention on your breathing, for example, and tune out everything else that wants to interfere, such as your own thoughts about the breathing, or any chit-chat about the happenings of the day.
In the second, you notice your breathing with a certain detachment, you become aware of it, acknowledge it and let it be. You don't concentrate on it. You simply witness its existence.
Also here you focus on the present, on the now. You watch, observe and notice everything that is happening at the moment without judgement or biased thoughts, and without trying to tune it out from your mind. Here, external or internal happenings are not distractions. They simply are.
Maybe the best technique that characterizes this type of meditation is the Zen meditation.
The more modern techniques can easily overlap in their meditation types. On your journey to learn how to meditate, depending on the techniques you are using at the time, you might find that some techniques can be both types of meditation: concentrative and non-concentrative at the same time.