Question about turing machines I've been reading a book about turing machines and it has a challenge about a building a Turing Machine that has as many 0s as many 1s but that can appear in any order. 

I don't understand how do you set the reading to the beginning and then make a transition to the beginning.

But it deals with only 0s that shows up before 1s, how would i go about in the same instance if i find something like 100, or 100001?
The Turing machine uses the tape alphabet $\Gamma = \{0,1,x,\epsilon\}$.
Writing down all the transitions explicitly is tedious, so I'll just summarize the main steps:


Move right until you find a 1 or $\epsilon$.
If a 1 is found proceed as follows:


Replace the $1$ with $x$.
Move the head back to the initial position (move left until you find $\epsilon$, then move right once).
Move right until you find a $0$ or $\epsilon$. If no $0$ is found reject.
Replace the 0 with $x$.
Move right until you find a $0$ or $\epsilon$. If no $0$ is found reject.
Replace the 0 with $x$.
Move the head back to the initial position.
Repeat everything from the very first step.

Otherwise, if no 1 is found:


Move left until you find a $0$ or $\epsilon$. If no 0 is found, accept. 
Reject.