|| means “or.” You can use it to provide a series of alternative expressions. Usually you want to put the alternatives in parentheses, like this: c(ad|ab|at)matches cad or cab or cat. Without the parentheses, it would match cad or ab or at instead
\ Escapes any special characters; if you want to find a literal *, you type \*. The slash means to ignore *’s usual special meaning.
Here are some more examples to help you get a feel for things:
c.pe matches cope, cape, caper.
c\ .pe matches c.pe, c.per.
sto*p matches stp, stop, stoop.
car.*n matches carton, cartoon, carmen.
xyz.* matches xyz and anything after it; some tools, like egrep, only match until the end of the line.
^The matches The at the beginning of a line.
atime$ matches atime at the end of a line.