As we describe it on the Loving Kindness page, Loving Kindness meditation is a practice which helps to cultivate the positive orientation of wishing well for yourself and others. In addition to the stabilizing elements of mindfulness, including breath and body awareness, Loving Kindness meditation makes use of imagery and language to help open the heart.
The imagery is what arises from bringing to mind people you're in a relationship with. You imagine their presence: what they look like, sound like; what it feels like to be in their presence. We often bring to mind someone we have a warm and intimate relationship with to help orient the heart towards kindness as it usually feels pretty natural.
The language element are phrases: simple wishes you repeat to yourself that help to orient the heart towards kindness. There are a set of "stock phrases" which are adapted in various ways from Buddhism which are usually used. For example:
May you be happy and joyful.
May you feel safe and secure.
May you be healthy and strong.
May you live with ease.
These are wonderful wishes but for many of us they might not sound very natural. Additional possibilities may open up if you had your own phrases of loving-kindness. The kind of language and sensibility that comes naturally to you.