Grants are available for undergraduate study, research projects, post-graduate study and teaching programs in the U.K. The British Marshall Scholarship and Fullbright Scholarship are grants that are available exclusively to U.S. citizens and cover the cost of things like airfare to and from Britain, tuition fees and maintenance costs.
If you secure a grant to study in Britain, make sure you have considered all the costs involved in studying abroad, particularly if you plan to bring family members with you. Research the cost of living before you come and bring extra money with you if your grant won't cover everything, to ensure that you will be able to complete your course. There is a lot of competition for British Embassy grants, so make sure you apply as early as possible if you want to secure one.
Contact your own country's education ministry and British Embassy to find out which grants are available to you and how and when to apply for them.