There are single word mantras which work on vibrations they create and bring forth into your life that you wish for . These are known as BIJA ( SEED ) mantras .
In this category , there are single word mantras to increase abundance in your life , to protect you from any accidents etc
There are mantras for Chakras in your body ( there are seven focal points within your body which control all functions of your body ) and depending on what part you wish to activate / enhance , you recite that mantra . These again are single word mantra .
The difference between the above two SINGLE word mantras is that the first set of single word mantras can be recited without any rituals at all and can be repeated when you are walking , driving , cooking etc ; in other words you can carry on your daily activities and at the same time you can keep on repeating the one word mantra . These one word mantras can be used singularly or in combination with another single word mantra .
In the case of Chakra mantras , because you are trying to activate a particular spot in your body , you need to sit still in one spot and repeat this single word mantra focusing all you energies to that part which you wish o activate / enhance .
It is said that in the West 60% of the adult population believe in horoscopes and will check their daily horoscope in the papers . As you know , horoscopes are based on the positions of the planets and predictions are calculated from there . Some planets move very slowly and may remain in you star for a number of years , thus influencing your daily life for a long time . There are phrase mantras for each planet that can be recited to appease a particular planet to start working favorable for you . These can be recited whilst you carry on with your daily chores .
There are mantras for specific ailments which are normally phrase mantras . There are mantras to remove obstacles from you path , there are mantras to bring in more wealth into your life etc etc .In fact there isn’t an ailment that can not be eased by mantras .
There are general mantras just to give you a peaceful mind .
And you do not require any elaborate ritual to use them nor do you need to understand them ; just experience its effect .
Sure you need to have a belief and a strong desire to change ; for mantras will work on your mind and body to bring about a different mind set to manifest that which you want.
It is you and your mind that will bring about the change that you desire , the mantras will help to create that right mind set .
More information on Hindu Mantras