How to secure yourself from the Central Security Service

What technical stuff [as in coded IDs] other than the MAC address and
IP address can reveal my who, how, what, when, where, why?

How would people know that it's me searching for stuff or visiting
websites/newsgroups?

You create a profile of yourself, and sooner or later it will,
if national security is involved, get linked to your identity.
If you use MS$ OS your machine will have a unique ID that
is used to check whether it is a legit or pirated OS and
whether you are entitled to updates.
So you need to build a machine that stores nothing
about itself, no bootstrap ROM, as pointed out toggle
in the bootstrap code, then get the OS off some media.
But then of course you possess the incriminating OS
media.
Building such a machine, including its OS and
network drivers is not a trivial task.
Once they are interested in you, you will be the
last to know.