Myriad means a lot of different things or a huge variety of something. Imagine if you go to a toy store and you see so many toys of different shapes, colors, sizes, and types! That's a myriad of toys. It's like having a lot of options to choose from.
Sometimes in school, the teacher gives you a myriad of homework to do. It means you have lots of different tasks to complete, like writing, reading, solving problems, drawing, or doing research.
Myriad can also be used to describe how many stars are in the sky or how many grains of sand are on the beach. It's an uncountable number because there are so many of them.
So, whenever someone says "myriad," it's like they're saying "so many things to choose from!" or "too many things to count!"