Mantra meditation gives the attention a single thing to hold — a sound, a word or a short phrase, repeated silently. For a good number of people that is easier than watching the breath, because there is something definite to come back to.
The traditional instruction is twenty minutes twice a day, sitting comfortably with the eyes closed. It is not a concentration exercise and it is not meant to be effortful: when you notice you have drifted, you return to the mantra, and the drifting is expected rather than a failure.
Mantra practice comes out of Hindu and Buddhist traditions, and some modern courses are taught within a specific lineage. If that matters to you either way, ask before you book what tradition the teaching sits in and what it involves.
