This year is the first year of the Multiplication and Tables check for Year 4 children. The National Curriculum (2014) includes a statutory requirement that pupils should be "taught to recall all multiplication and division facts up to 12 x 12" and knowing their tables will really help your child make progress in Maths.
I have added some links that you may find useful and give you a better idea of what the tests involve and how you can help your child learn their tables. There are also lots of apps available, as well as well as the Topmarks website, to help children learn (the fun way!).