Field Extension and Minimal polynomial

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Below is example of extending Field $F$ to include root of a irreducible polynomial. After extending Field $F$ to ploynomial Field $F[t]$ , we take polynomial $p=t^{3}+t+1$ and declare it is equal to zero in that polynomial ring. It makes

$t^{3}+t+1=0$ so it leaves

$t^{3}+t^{2}+t+1=t^{2}$

After all the subsequent subsitution it will leave only the first,second and third row. My question is

How the other elements of row 3 are eleminated. I only understand the above two subsitution. How will the further subsitution works?

Roots of this polynomial is $t$, how?

Is the polynomial is minimal polynomial? example