27 March 2017 Last updated at 13:50 BST
When people say mental health, they are talking about how people think and feel, and how they are coping with things that are happening in their life.
As Dr Radha explains, it's perfectly normal for us to feel worried or anxious from time to time, but when those feelings don't go away, that's when you might be struggling with a mental health problem.
Poet and author Michael Rosen explores how it is really important that people feel they can talk about issues like this in this guide.
To find out more about what a difference it can make when people are able to open up about having a mental health problem, watch Inside My Head: A Newsround Special and find out how talking about his problem changed 14-year-old Josh's life around.
BBC Radio 1's Dr Radha explains why it is so important to look after our mental health.