Hi,
When you try to access multiplayer, are you unable to select it?
If so, you are a child. If so, you need to ask your parents to allow access through the family access system, if it's active.
[Link to Minecraft article: https://help.minecraft.net/hc/en-us/articles/24302916594701-Managing-Multiplayer-Game-Access-for-a-Child-Account-in-Minecraft]
Give feedback if the information was useful or not.
Thanks