I have been asked with a task that is about linux driver development and its so complex actually. I'm in the first two months of work, and I don't want say I do not know about this and my boss expects so much about me!. I'm trying to read books but just skimming the pages, and can't focus, I don't really know what to do.
If I was a junior and realised I was in over my head, I would let my boss or team know as soon as possible. The longer you leave it, the longer they will think everything is fine and the bigger impact to them when they finally find out you haven't completed the task.
Even now, in pretty senior roles, I would still ask for clarification or help on a topic I don't know.
Be up front about it. Let your boss know what aspects you can cope with and what bits you need help with.
When you're in over your head, let your boss know, as Rory says, but do more than that, and try to do it first. Break it down into smaller chunks of tasks, figure out what you can do and what you need help with. Show your boss what you have, what you think you can handle, and what you need help with. Hopefully he can break some of those tasks down for you too.
You can't focus because you don't even know where to start, so try to start by figuring out not how to do it, but what even needs to be done. The more you know, the more you'll be able to focus. And when you've figured out some of the easier steps, you'll gain confidence to grab the harder ones.