How to choose the appropriate public (i, m) and private (j, m) keys?
I assume that $m = pq$ (85) is the modulus, and the number you computed (64) is $\phi(m)$. Now we must choose the exponents ($i$ for public, $j$ for secret? , weird notation) in such a way that $ij = 1$ modulo $\phi(m)$. In fact we can work modulo 16 if we like, because that is the least common multiple of $p-1$ and $q-1$. So if we choose $i = 3$, we choose $j=11$, as $33 \equiv 1 \mod 16$. Or $i=11$, $j=3$, this is symmetrical. Or we could choose $i = 5$ and then $j=13$ works, or vice versa again.

Then encryption of a number smaller than $m$ is exponentiation to the power $i$, modulo $m$ and decryption is exponentiation to the power $j$, modulo $m$.

Of course these numbers are way too small to provide any security, but that's the general idea.