Lion’s Roar has a page on their website that provides introductory information on metta and links to a number of more detailed articles and guided meditations on that topic. You can find their article here: Loving-Kindness
Joanna Hardy discusses metta and the way you can practice it in meditation and in daily life. She also describes her initial reactions to metta practice, which you may find encouraging and useful, if like Joanna, you think the idea of practicing lovingkindness meditation is “a little too mushy and sentimental for [your] pragmatic mind”. You can find her article here: How to Practice Loving-Kindness
Jack Kornfield has a short description and guided meditation for metta practice that you can find on his website: Meditation on Loving-Kindness