base 10 is just the ordinary number system we use. Just put 2^12 (2 to the power of 12) into your calculator.
For base 2, you need to express it as:
a[n] 2^n + a[n-1] 2^(n-1) + ... + a[1] 2^1 + a[0] 2^0
where a[n] is a non negative integer less than the base. In the case of base 2, that means a[n] is 0 or 1.
In the case of 2^12 then, it's easy. You want 1 x 2^12 and everything else zero, i.e.
1 2^12 + 0 2^11 + ... + 0 2^1 + 0 2^0
So you write these digits like in base 10, with the least significant at the right, i.e. 1 followed by 12 zeroes. (A 1 for the 2^12 column, a zero for the 2^11 column, a zero for the 2^10 column, a zero for the 2^9 column ... down to a zero for the 2^0 column).
i.e. 1000000000000
For base 2, you need to express it as:
a[n] 2^n + a[n-1] 2^(n-1) + ... + a[1] 2^1 + a[0] 2^0
where a[n] is a non negative integer less than the base. In the case of base 2, that means a[n] is 0 or 1.
In the case of 2^12 then, it's easy. You want 1 x 2^12 and everything else zero, i.e.
1 2^12 + 0 2^11 + ... + 0 2^1 + 0 2^0
So you write these digits like in base 10, with the least significant at the right, i.e. 1 followed by 12 zeroes. (A 1 for the 2^12 column, a zero for the 2^11 column, a zero for the 2^10 column, a zero for the 2^9 column ... down to a zero for the 2^0 column).
i.e. 1000000000000