The British government is like a big game of pretend where grown-ups with fancy jobs play make-believe to run the country. The frontbench is where the most important grown-ups sit to pretend to do the most important jobs.
Think of it like a big fancy table at dinner time. The front row is where the most important guests sit - this is where the grown-ups running the country sit.
Each important guest has their own pretend job to do. The Prime Minister sits at the head of the fancy table, like the grown-up leader of the pretend game. The other important guests sitting next to the Prime Minister are like the Vice-Leaders, they help the leader run the pretend game.
Then, there are other important guests with their own pretend jobs, like the pretend helpers for things like money or health or education at the fancy table.
All of these important guests sitting at the fancy table together make up the frontbench of the British government, where they pretend to do their important jobs and run the country.