Experimenting:
Yes, it is a backslash in front of the frac command.
\frac{Numerator}{Denominator} gives
E.g. \frac{1}{2} gives .
The backslash is usually located above the enter key.
The radical symbol is given by
sqrt{Something}
which gives
.
E.g. \sqrt{2} gives .
If you want a higher root, like a cube root, then you'd put
sqrt[n]{Something}
to gives
.
E.g. \sqrt[3]{4} gives .