How to write the turing machine processing operations? I have this Turing machine example given in my book:

For the language $0^n1^n$. I understand how it works because it's very similar to a Finite State Machine.
But what I want to know is the following:

What is the $|-$ symbol is for what are the states $q_0$, $q_1$ doing in middle of everything. Unfortunately my textbook doesn't explain any of it.
The state marks the position of the head (as well as the current state): for example, in $q_00011$, the head is to the left of $0011$, and in $xq_1011$, it is to the left of $011$.

The notation $\sigma \vdash \tau$ means that the configuration $\sigma$ leads, after one step of the Turing machine, to the configuration $\tau$.

As David Richerby mentions in his comment, all of this is explained in your textbook at some point.