When you think, act, or speak with loving-kindness (metta), you act are kind, open, welcoming and accepting towards other beings or processes. You wish them well. You are not clinging. You are charitable and have a kind feeling towards them. Eventually, you develop a deep friendliness towards beings. Metta is like friendliness, but whereas we are "friendly" towards another being, metta is just impersonal "friendliness".
There isn't a word in English that expresses metta, so explaining metta is a bit long winded. The following story from Persia illustrates metta.
The Persian poet, Rumi, gave an analogy using a boarding house. At the boarding house, everyone is welcome. When there are rooms, it is always open. Everyone is always welcomed in a friendly way. They stay, or go, as they wish. The landlord treats them all the same. He does not become attached to them. He knows they will soon leave. If they are somewhat awkward, the landlord does not care. They will soon be gone, and others arrive. All are welcome and all are treated in a friendly manner.
Metta is like the owner of a boarding house. It is always open. Welcoming all in a friendly manner.
When meditating on metta, you can use all the four thoughts, or you can use them one at a time. That is using all four each time you radiate metta to a dear person, neutral people, enemies, and everyone. Or you can go through the list for each question, going through four times. The older translations use the following:
May all beings:
A more modern version is:
May all beings:
You can use your own words. And you might make these wishes more specific for specific people. For instance, "May Tom pass his exam."
You can use Metta in relation to anything. That is, the feeling and attitude. But these exercises are meant to be used with living people as the object. You can welcome with Metta and without clinging, the image of someone no longer with us, if the image arises in the mind. However, these questions are not applicable to non-living things. For instance, you can radiate the thought and feeling, "Be healthy" to living beings only.
Buddhists sometimes practice metta as a remedy for ill will (and is linked with Right Intention). They can also use it as a general remedy for aversion.
For instance, they can welcome discomfort lovingly. This is like the Christian St Paul saying, "Gladly therefore will I glory in my infirmities". In Buddhism, this is a remedy for the discomfort of aversion. The idea is to block craving, not to like pain! If you are openly welcoming discomfort, you cannot be make it worse by trying to make it go away. You try to make it go away because you don't want it, which is craving. Craving is the origin of suffering. So by trying to make something go away, you increase suffering, and make the suffering worse.
In some systems, Metta is used in wisdom and concentration. When used in concentration it is used to develop peace and serenity (and concentration). It is then used with compassion, sympathetic joy and equanimity.
Settle yourself comfortably to practice
Keeping the eyes closed, repeat the word "metta" a few times and think about its significance: love as the opposite of hatred. It is a profound feeling of good will, sympathy and kindness promoting the happiness and well-being of others.
Imagine your face with a happy smile, and smile. When you are happy, you cannot be angry or have ill will or hostility.
Now, think: "May I be free from enmity, free from affliction, free from anxiety; may I live happily." When so filled with love and happiness, you are ready to overflow it to others.
I visited all quarters with my mind
Nor found I any dearer than myself;
Self is likewise to every other dear;
Who loves himself will never harm another (S I 75)
Next, visualize someone who you love (not romantic love) and admire, such as a teacher. Alternatively, you can think of a baby or a puppy (something you have tender feelings towards. Avoid using a romantic lover, when beginning, because this taints metta with Earthly love. You should build up a state of loving-kindness, not romantic love, so you can radiate it to others.
Think of others, perhaps parents who you regard highly. Think: "May they be happy, free from hostility, health, and free from distress."
Visualise these people before you and visualise rays of love going from your heart to them. You do not have to "see" them, just know they are there.
Radiate the thought to each one: "May they be happy! May they be safe! May they enjoy good health!" May they be at peace!" (Use he or she as appropriate!)
You can use any thought that represents loving kindness. "For instance, may they be joyful and safe!"
A dear person, with whom you have had a quarrel should be included later when meditating on those to whom you have ill feeling.
Next, visual neutral people, those you do not have any feelings towards, such as acquaintances, people like the postman, and shop assistants. Visualise them and visualise the rays of loving-kindness going to them.
Lastly, visualise people with whom you have some ill will. See them as happy and smiling and receiving your loving-kindness. Naturally, you will do this only if there are such people.
Finally, imagine or know that all beings are before you. Radiate lovingkindness to them all.